I assume both warming up and insulating the toilet seat from the skin will give the same comfort.
1.
Socks Place socks on either side of the toilet seat.
This will prevent the direct contact of buttocks with the toilet seat, but there are some risks involved in it as the socks may get germs, so be sure to wash them afterwards.
2.
Toilet paper Fold the toilet paper three or four times and place it on one side of the seat, ensuring that it covers one side of the oval seat.
Do the same for other side.
3.
Rub with Napkin Rub the seat with towel napkin until it warms up to the satisfactory level.
4.
Artificial seat made of cloth Stitch a seat shaped material with some thin layer of insulating material.
Have some sets of this.
Replace it daily.
lifehacks.stackexchange.com/users/115/Joachin Joseph
I sit on it for a few seconds with my pants on.
This lets enough heat transfer that it warms up, but not so much that its unbearable.
lifehacks.stackexchange.com/users/4666/Bowen
A porcelain toilet feels cold because porcelain is good at transfering heat.
You can buy plastic or wood toilet seats : this is a ring that is placed on top of the toilet, and attached to the toilet via a hinge.
Plastic and wood don't transfer heat as easily as porcelain, so they don't feel as cold.
lifehacks.stackexchange.com/users/5307/Hobbes
Just use about 1/4" thick of foam from appliances, cut out a shape to fit your toilet seat.
Remove and hang it up after each use.
lifehacks.stackexchange.com/users/18381/Mai Nguyen
If you have a minute to spare before sitting, try using a blow dryer, otherwise known as a hair dryer, on it.
That should work pretty well, but only if you aren't dancing from holding it in.
A prevention method, and not really a hack, is to buy either a heated seat or one of those cushioned seats which will still be cold but should warm up much faster.
lifehacks.stackexchange.com/users/2281/Doug Watkins
Soak toilet paper with hot water.
Rub the toilet paper on the ring of the seat and squeeze out the water.
Then dry the toilet seat.
The toilet seat is now warm.
lifehacks.stackexchange.com/users/11515/NutBuster69
Three rather simple methods you could use before/instead of sitting down on the cold seat: Preheat the toilet seat by rubbing the ring for a while using your hands Add some insulation , like covering the ring with toilet paper Avoid sitting on the it , squat over it like they do in some cultures
lifehacks.stackexchange.com/users/4490/holroy
I took a heating pad we weren't using anymore.
One of the long kind and not the short heating pads.
I tied it around the toilet lid with the majority of the pad facing the toilet seat.
The heating pad has two straps on each end, so I tied them together on the back (top) of the lid.
Now, everyone must close the lid regardless of user's gender.
I plugged it in at the sink outlet (I also swapped out the standard outlet with a GFI).
I set the heat control just a tad before the lowest setting.
In other words, when it was on the lowest setting (one)
it was too warm ( like hot), so I turned the dial more towards the off position, to where it's just registering 'on'.
Perfect!!.
I leave that puppy on 24/7 for the most part because you never know when you have to go.
The women love it and I sit regardless of my purpose for using the toilet.
Long gone are the days of having to stand just to conform to social expectations.
An added plus is no more splatters to clean up.
lifehacks.stackexchange.com/users/23757/David
A very cheap and effective method that I have used while living in the mountains, is to use a tennis ball.
Keep the tennis ball next to the toilet, and before you sit down, vigorously run the ball along the seat.
Press down hard, because the key to warming it up is to create heat from friction.
With practice, you can get the seat nice and toasty in about ten seconds.
lifehacks.stackexchange.com/users/23805/Eric1975
We use to wash it with boiled water to keep it warm in winter season.
lifehacks.stackexchange.com/users/2807/Rajnikant Sharma
I always switch the waterline on the back to the hot waterline.
if you don't have one by a flexible cord and go in the basement switch it around
lifehacks.stackexchange.com/users/13117/Rod Farva
The ultimate solution for this is a electric bidet toilet seat .
It is more hygienic and after you wash your anus
you can warm your back just pressing a button!!
It's awesome and reduce the using of toilet tissue paper as well as your cost.
lifehacks.stackexchange.com/users/20110/Sharon Ream
In the winter, the porcelain toilet seats can get extremely cold and are just unpleasant to sit on in the event that 'doody' calls.

Is there a quick way to warm up the toilet seat to make it more comfortable to sit on?
How to quickly warm up a toilet seat
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<temperature><bathroom><comfort>
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lifehacks.stackexchange.com/users/2089/MrPhooky
There are a number of ways to quickly warm up a toilet seat. One would be to cover the seat with something, such as toilet paper or socks. Alternatively, you could rub the toilet seat with a towel napkin until it's warm. Another option is to simply blow the toilet seat with a hairdryer or, in fact, sit on it with your pants on for a while. The options are to place socks or toilet paper on the seat, rub with your hands, a cloth or a tennis ball till warm, make an artificial seat out of cloth, sit on it in pants until warm, get a plastic or wooden seat, make a foam seat cover, warm it with a hair dryer or with toilet paper soaked in hot water or fit an electric heating pad.
Try placing socks on the toilet seat or toilet paper or rub with a napkin until warm or make an artificial seat out of cloth and replace daily. Sit on it with pants on until warm. Buy a plastic or wooden toilet seat. Cut out a seat cover from a foam sheet. Warm it with a hair dryer. Soak toilet paper in hot water and wipe the seat. Rub the seat with your hands, add insulation, cover with toilet paper, try squatting without touching the seat. Attach an electric heating pad to the toilet lid. Rub the toilet seat with a tennis ball. Wash with boiled water. Use an electric bidet toilet seat.