Getting guitar lessons with a good teacher would be the first choice, but if you really can't have a teacher, then watching guitar video lessons online would be the second choice.
You have to be careful though, there are many guitar players posting lessons on Youtube, and not all of them are good teachers or even good players.
One of the best online teachers would be Justin Sandercoe.
He has a complete beginner's and intermediate course, plus he's a pro musician and has been teaching guitar for many years.
His website is http://www.justinguitar.com .
Also check out the links given by Dr Mayhem, they contain some useful information as well.
One more thing, you mentioned that you would like to learn to play by ear.
Justin Sandercoe explains it on his website, but to play be able to by ear, you have to start by learning to transcribe music, which basically means listening to a song or a solo and figuring out the chords and notes by ear.
music.stackexchange.com/users/974/Daryl L
You'll probably want to look at Need help in starting to learn guitar
What is the first scale one should learn on the guitar Is there any guitar tuition software...?
And there are a lot of other good questions tagged guitar and learning
music.stackexchange.com/users/104/Doktor Mayhem
Music is communication.
They've found that when you play with other players, the parts of the brain that deal with speech light up.
You can get somewhere playing by yourself, but you get farther faster when you play with someone else.
It doesn't have to be in a lesson context.
Plus, when you play with someone else, you get a strong sense of what needs attention.
You may think you want to do fancy flatpicking runs, but you'll know you need work on timing and changing chords cleanly before picking up double-down-up picking ever need show up.
music.stackexchange.com/users/195/Dave Jacoby
I think that with your background, you can educate yourself.
But at first it might be helpful to get a few lessons from a professional guitar teacher in order to teach you how to place the fingers of each hand to execute the notes correctly and produce the proper tone.
You will also need a critique of how you sit, stand and hold the instrument to enable playing with the least amount of fatigue, and factors like that.
A surprisingly difficult problem for many players who come from an instrument where you only play one note at a time, such as woodwinds, is this: You can form one chord on a guitar, and you can form another chord on a guitar, but how to you get your left hand to move from one chord to the next chord in the tempo of the song?
You want to hold one chord for its full rhythmic value and then, in an instant, form the next chord just a fraction of a second before the next chord needs to sound.
This is something else that a teacher could help drill you on.
music.stackexchange.com/users/None/
In this day and age - learning from youtube is not a bad idea.
There are many helpful tutorials you can find there.
Also, try learning a song that you really like and that has easy chords.
This way you'll be motivated to practice more.
I would recommend beginning with chords and then moving onto finger-picking, unless you wanted to play classical guitar.
music.stackexchange.com/users/1292/reepicheep
I saw a really great set of videos on how to play the guitar from Brazil on Y-Tube.
Subtitled in English -- it's free form and breaks it various styles down in rhythm and chords for you -- perhaps a different style for learning that you might find nice as an alternative.
music.stackexchange.com/users/1043/Alice
If your already a player of other instruments, and an accomplished musician, the the first advice i would give you is to transpose some of the music you know on the other instruments onto the guitar.
You should be able to do this by ear, note by note if need be.
Transposing scales/arpeggios and such by ear shouldn't be a problem for you, just remember that once you have transposed a scale in a particular key, to remember the shape, as on the guitar the shapes stay the same across all keys.
Your major learning curve will be chords, fretting them on a guitar can be quite difficult to begin with.
In your position, I would choose a simple song/piece i was familiar with, and learn/apply the chord shapes for the guitar, if you have a good ear
this shouldnt be a problem.
Then build from there with another song, or write something with what you have learned etcetera.
Same applies with chords, once you have learnt a shape
, say one of the minor triad shapes, it stays the same regardless of the root.
music.stackexchange.com/users/149/Bella
Learn and Master Guitar goes through the basic to the fundamentals of playing by ear.
http://www.learnandmaster.com/guitar/
music.stackexchange.com/users/790/MdaG
One idea that I don't see mentioned here often for people just getting started on guitar is to enroll in a community college beginning guitar class.
The cost is much lower than individual lessons, basic questions get answered, you have a chance to get to know others who are also just beginning, you won't be the only one making mistakes and having trouble, they only last for a semester, and they can be a lot of fun to participate in.
And they usually have evening classes for working adults.
You won't be an accomplished player when the semester is over, but you'll have the option to continue advanced classes or study on your own.
music.stackexchange.com/users/44636/skinny peacock
I have an acoustic guitar that I've tried to learn to play many times. I'd like to learn to play by ear... I'm an accomplished musician on several other instruments but those are all woodwinds and I've used music reading. What's the best way to really start out? I've used books to no avail. Thank you!
How to learn guitar without physical lessons?
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music.stackexchange.com/questions/3593
music.stackexchange.com/users/1011/TeeCee
Getting guitar lessons with a good teacher would be the first choice, but if you really can't have a teacher, then watching guitar video lessons online would be the second choice.  In this day and age - learning from youtube is not a bad idea. Justin Sandercoe explains it on his website, but to play be able to by ear, you have to start by learning to transcribe music, which basically means listening to a song or a solo and figuring out the chords and notes by ear.   Learn and Master Guitar goes through the basic to the fundamentals of playing by ear. There are two key ways that you may be able to learn to play without physical lessons. One will be to look for tutorials online, such as on YouTube. The other will be to try and transcribe songs for guitar, particularly songs that you can already play on another instrument.
Looking for YouTube tutorials might be a good way to get started initially. Transcribing music for the guitar will be a good way to learn by ear.