Do you want to play an instrument, or do you just like the idea of playing an instrument?
Go to a musical instrument store with a lot of kinds of instruments. I don't mean "a lot of different guitars," I mean a lot of different kinds entirely. Things you've heard, things you've never even heard of before; the more options, the better. In fact, go to more than one shop. Go back to the same one if you want, go to others if you get bored.
Poke around at different instruments until you find one you like playing with. Not "playing" in the sense of "making a song come out;" playing with. Maybe it'll be something with strings; maybe it won't be. Whatever you do, don't load yourself down with preconceptions and expectations about what you should like.
For the first month or month and a half after Anna gave me her mandolin - Summer, the mandolin I perform with now - almost all that I did with it was poke at it at funny angles and strum it with all strings open. Then I'd try to play Great Big Sea's "Goin' Up," or the traditional song "Lukey" a few times, and generally I'd just go back to making it make noises. For five weeks or so, that was mostly just open strumming. No chords, no strings held down, just strum.
You want to find the instrument where when you try something like that, it's fun, and doing it more also sounds fun. Forget your ideas about "proper" instruments and for the love of the gods don't let your preferences in musical genre dictate the choice. Maybe it'll be a ukulele! Maybe it'll be bells. Maybe it'll be a theremin. Maybe it'll be a flute, shakuhachi, or whistle. Maybe it'll be a string-plucked washtub bass. Maybe it'll be a beatpad, or a 10x10 sequencer grid. Maybe it'll be a balalaika. None of that matters. Forget everything else and just find the thing with the noise that makes your brain go "....oh!"
That's what my brain was doing with the open-strumming thing for five weeks. The sound was working its way into my brain, and it felt great.
After you've played with something like this a few times, buy it, take it home and just keep playing with it. Not "play it" - play with it. Just play with it, without expectation, and let what happens, happen.
If after a while you want to try to play a song, make one up. Find a sequence of noises that sound good and play with them until you think it's a song. Guess what: it is! (Maybe you stole half of it from somebody else: great! Just don't try to copyright it. ^_^) Or, if you'd rather, pick one song you like a lot, look up some videos on youtube that introduce you to the basic concepts of playing whatever you've got, and try to echo what you hear in the song you like. Don't start drilling on scales or whatever if you don't want to; that can wait until you're hooked good and proper and actually want to do that.
It's not school. It's not work. You aren't being graded. You aren't being paid. You don't have to do it in someone else's order. There is no GPA at stake. There is no performance review. You'll make ugly noises. You'll screw up. That's fine. Throw all that away and just find the noise and the toy you want to play with, and play with it however comes to mind.
And maybe you'll get bored, and maybe nothing will happen. Or, maybe something amazing will. Find out.
This post originated at ソ-ラ-バ-ド-のおん: Solarbird Makes Noises, on Dreamwidth.