The Unicyclopedia/Trials

Trials is about controlling where you are and where you want to be.
Practicing trials.
When you practice trials, it is important that you have a good unicycle. It should be able to stand your riding. It is also important that you do not hurt yourself. Dropping huge heights will only hurt you and your unicycle. I personally feel that your trick should not be somewhere where the risk of getting hurt is very high: The challenge should be the obstacles and not your fear!
When practicing trials, also try to have somebody to watch you and see if you are doing it right. It helps a lot to watch movies or learn from a friend. Rest is also as equally valuable as practice when it comes to learning new moves. Give yourself plenty of time for both, and take breaks if you need to.
Essentially, to ride trials requires an intensively focused state of mind. An individual's ability to perform various trials moves stems not from the limits of what has or hasn't been done, but from what their imagination, and body will permit.
Crank grabs.
A crank grab typically consists of two steps
It is important to lean far into the object you are grabbing onto. The second foot may or may not leave the pedal. Practice doing small hops from the crank before trying to go fully to rubber, and it will follow naturally. It may take a while before you learn to land on the crank in balance.
A good way to learn crank grabbing is to practice just from the part after the crank has been caught on the ledge. First, just try to get the wheel over without focusing on landing on the pedals with balance. Next, focus more on landing with control over the unicycle. Continue this method until you can land the crank grab easily. Now is the time to learn the actually grab section of the crank grab. Finally, you can put it all together!
Pedal grab.
A pedal grab is typically made seat out and consists of two steps
It is important to lean far into the object you are grabbing onto. This is more difficult for the pedal grab than the crank grab since the seat isn't as stable. The second foot may or may not leave the pedal. Practice doing small hops from the pedal before trying to go fully to rubber, and it will follow naturally. It is in fact easier to go from pedal grab to rubber than from crank grab to rubber once you know it.
Try to think of it as a skateboard ollie. This was the tip that made me go to rubber for the first time. Lift your free pedal (the one not on the object) a little bit up in the air and then in one single motion swing the other pedal up. The key to succes is to practice. If you follow these steps you will learn to pedalgrab in hardly any time.
High hop seat in.
It is difficult to hop high seat in (other than using seat in rolling hop). Accept it to be difficult to get higher than 30 cm unless you use pre-hops. Practice bending at the waist and pulling the unicycle up as you hop. For higher seat in hops, a pre-hop is necessary. You would typically also run a higher tire pressure and lower seat height than normal. It is possible to get up and over 60cm seat in side hops, however the majority of unicyclists will either switch to seat out or to rolling hops. 
Seat-In hops are essential to learn before seat-out hops, since the seat provides an extra point of contact, and therefore more control for beginners. After the seat begins to limit hopping height it is recommended that one develops his/her seat out control.
High hop seat out.
When hopping seat out, it helps to have the seat at a comfortable height. It should be just high enough to let you stand almost straight while holding the saddle in front of you. Holding the saddle in the back makes it easier to pull it up. Practice hopping on angled surfaces, or doing natural trials to learn controlling rotational force on the wheel. The key to comfortable hopping seat out is even pedal pressure distribution. If one is unable to apply even pressure, then the wheel will roll uncontrollably.
Hopping seat-out requires several different aspects in order to attain maximal height. This technique can be broken down into the following:
1. Prehop
2. Jump
3. Landing (tuck)
4. Recovery
1. Practice pre-hops by bunny hopping seat out and focus on the timing, you will develop a sense for when force should be applied. Prehops can be transferred from hopping seat-in, since it is the exact same action, and will transfer directly. To execute the prehop, back off a bit from the object, stand still, make a hop towards it, and as you hit the ground, apply pressure at the right instant, and the force will bring you up while you pull up the unicycle beneath you.
2. The jump is where you're actually jumping. One's ability to perform high hops depends on one's vertical jump, but only to a certain degree. Vertical jump is the height an individual can jump off the ground(measured from where you can touch a wall, arm fully extended to where you can touch the same wall when you jump up) It makes sense that vertical jump affects hopping height, however this isn't the only factor, and one's Vertical Jump can be improved through fitness and just practice.
3. The Landing is the most important part of the high hop. This requires a tucking off the wheel up underneath you as much as possible. Make sure you pull the tire up as far as possible to get maximum height. When you reach the top of the object you're aiming for, you should almost be able to feel the tire hitting your butt. Using this technique with a static hop it is possible to get over 85 cm (2.77 feet). With a prehop done properly, you should be able to add 15cm (6 in.) to your static hop. Using this technique hops of over 100cm (3.25 feet) have been accomplished.
4. Recovery is basically standing up from that super-tucked position that you used to get onto the object which you just made it up. This seems like an unimportant step, but if you can't stand up, that massive wall you just cleared doesn't mean anything, except that you can "Almost make that hop"
Finally put it all together. 
Also check Ryan Atkins video tutorial on how to hop somewhat high.
Gapping seat out.
Stand perpendicular to where you want to go. Lean to the side you with to go, and make the hop. Gapping seat out will allow you to pull the tire up as you jump, and this can be used to achieve a greater distance in your gaps much the same way as in regular seat out hops. It is a lot easier to gap to the sides than it is to gap forwards. You will develop a sense for how much you need to lean before jumping; it is usually not that much. It may help to twist in the air, meaning to take off to the side and twist in the air so that you land facing the direction in which you jumped. If you are gapping onto a narrow object, try to gap somewhat less than you think you have to and use the momentum from the jump and shift your hips to find balance. It is somewhat easier to do the adjustments when you jump too short than when you overshoot.
Gapping seat in.
Similar to gapping seat out but with some more control.
High rolling hops.
Initiation:
When working out how far you need to be before starting a rolling hop, take the height of the object onto which you wish to hop, and turn this into the distance from which you will initiate the hop. Add a little bit more to the distance at which you initiate the hop. Start riding backwards about 3-8 revolutions (depending on personal preference and situation) from where you wish to initiate the hop. 
E.g. Bob wants to rolling hop onto an 80cm high table. He works out where he would initiate the hop, about 90-100cm from the table to (horizontally). He then puts the center of his wheel onto the spot, rides backwards 6 revolutions and stops. He puts a rock at where he has stopped so that he can adjust how far he needs to be if further attempts are made. Bob then rides as quickly as he can to the initiation point, holding his seat and preparing himself as he approaches. He then pulls up on the seat, using his other hand for balance and stability, and launches himself up as hard as he can. As he approaches the table top he bends at the stomach, bringing the wheel up in line (vertically) with his head. The continuing horizontal momentum will carry his body onto the table with the unicycle. 
The key to Bob's success however, was in the fact that he had progressively practiced the rolling hop everyday. It doesn't just happen!!! Also, when doing a rolling hop, the majority of people bail (pull-out) because they feel that they cannot make the hop. The key is, just do it. If you stack it, make sure you have safety equipment on, but in the scheme of things, you must make yourself do it. 
"I recently made a couple of 80cm rolling hops, and I found that the first attempt that I made it was a complete surprise, because I just forced myself to do it! Also, if you feel like after about 15-30 minutes that you are still not making it because you are too afraid/scared/unwilling etc... leave it for a day, or a couple of hours, go and do some wheel walk/gliding/backwards riding/backflips for a while and come back to it later. Also, if you keep trying rolling hops at the same place and still get scared, try doing it somewhere else. And remember, once you have made it, convince yourself that you can make it every time from now on. Also, it is a good idea to measure the height, and compare it to other situations of the same height when in doubt of whether you can make it or not." - UR
Dropping seat in.
Dropping seat in is the easiest way of dropping. The most common way to drop seat in is to just approach the edge and then "kaboom" down to the ground. This produces tremendous stress on the axle. Instead you should try to hop forward, bending your body slightly at the waist to help the wheel roll forward with you as you hit the ground. It is important to have some forward motion, so as not to end up on your butt as the wheel shoots forward.
Having the seat lower than you may help when attempting seat-in drops by avoiding the squishing of gentleman's bits. Soaking up some of your downward momentum upon landing with flexing of the upper body downward is a good technique to take load off of the axle and the knees and ankles.
As you get better you may roll off the obstacles instead. It is good to practice dropping in both stances.
Dropping seat out.
If it is not possible to roll out a drop, dropping seat out is an effective technique. Seat out drops can also be combined with a roll out if the surface allows. Seat out dropping provides a way to drop onto objects like fire hydrants or gapping bars since you may bend down to absorb the downward forces. One crucial thing is to keep the wheel stable through the drop.
Riding down stairs.
When you ride down stairs, you want the unicycle to be slightly in front of you while at the same time you want to lean forward. It is easiest to bend a bit at the waist. If you lean backwards chances are that you will fall on your back, and if you lean forward, you are likely to leave the unicycle behind. Also, stairs are easier to ride and much less intimidating if you think of them only as a bumpy hill. 
The next thing is that you should keep some distance to the seat so you do not hurt yourself. Suspend in your knees if needed, but the need to suspend is not as big in steep stairs.
Riding down stairs is a little dangerous if you do not use a helmet and other protective gear. Protect your back as well as you can, the chances of falling backwards are quite high. Also be aware that you might end up running down the stairs instead of cycling.
The biggest thing that helped me was pulling up on the seat! This keeps the pedals stuck securely to your feet preventing you from simply coming off your uni.
Mounting on skinnies.
If the rail is low enough, put the wheel of your uni up first, then one leg (the one that will be on the rail as you mount). Hold the seat with one hand and keep the other out wide for balance. Step up and regain your balance. Then get your pedals where you want them (I've found the static mount is easiest so have the pedals horizontal) and put one foot on the back pedal.
It's easiest to balance if the back foot that's still on the rail is at about 30 degrees or less to the direction of the rail. If your foot is at more of an angle there won't be as much shoe in contact with it and you won't be able to correct your balance as easily, plus depending on your shoe type, you might get stuck in the arch of the shoe and that will make it even more difficult to balance.
When you're in that position have the seat between your legs as you'll be much more balanced that way, and stand there for a few seconds making sure your weight is directly over the uni and the uni is directly over the rail. This is a very important step. Have one hand on the seat when you mount so you're absolutely sure it goes where you want it and you don't have to fix it later while you're trying to ride the rail. 
You MUST completely ignore the terrain below the rail. That is what's most likely to make you mount and lose balance to one side even if it doesn't intimidate you. 
Then mount and bring the other hand out wide for balance, and ride the rail.
Riding on skinnies.
Once you are steadily mounted, pedal forward slowly. It is important to look at the end of the skinny, not directly down at the tire. Try thinking about pushing on the pedals as lightly as possible, so your wheel does not wobble. Like almost any other skill, it helps to keep your weight on the saddle.