I am currently making a game as a hobby (role: programmer, designer, and writer), so I'll answer based on what I know:
As has been stated before, you need to be able to do something.
Programming, art, music, etc.
something. If you can't do one thing, you can always hire somebody else who can, and that essential thing you have will be the foothold for directing the project if game design is really what you want to do.
"Game Design" as a skill, alone, doesn't count. The people who actually have other skills can do design without you, and they'll probably end up better at it by virtue of spending time hands-on with the game. Almost every nerd on the internet is an armchair game philosopher these days who will run their mouth off for pages if you ask them about anything (I'm guilty of this, I admit), but don't actually have any true experience or understanding of what it's like to design a game (not guilty of this anymore!). Quite frankly, the real game design experience is the 2000 hours you'll spend meticulously tweaking and balancing your game, and you can't do that in no armchair. I've spent 1800 (this is a real number and I'm cutting it short!!!) hours on my game and I'm only now just finishing up the first stage.
So yeah, learn to program, learn to draw, or learn to compose music or sound fx. Learn to do something that'll make you useful to a team or it won't happen. And remember that whatever you choose to do,
it won't be fun. You need to be operating out of
passion. A drive that keeps you going with sheer unshakable
determination even when you really fucking hate it and feel utterly crushed with depression and anxiety. Otherwise you'll get burned out and won't finish.
If it's any consolation though, there will
also be moments of intense fulfillment, excitement and joy in accomplishing goals and realizing your creativity.
Also keep in mind that finding other people to work with you probably won't be free. When I first started out, I was under the illusion "I'm willing to make a game for free, so surely I can find artists and musicans who share such a passion and will do the same!!!" Ha ha ha ha, how naive. No. There are a few people like that but they're rare. You're most likely going to need to commission peeps. Though depending on what type of game it is, that might not be too bad. Decent sized sprites tend to go for about 30$. Not too bad for a shmup or platformer if you're judicious. Though if you're doing a fighting game and need 300+ sprites per character....yeah...
Oh and unless you're game is a visual novel, writing doesn't count either.