Strange random post here, but it's something I've been thinking about as I've been doing commissions lately. I know some programmers might aspire to be game developers here, so here's just a little mini guide from the other side!
It's great to tell the artist you wish to hire about your game! It's better to give a brief synopsis and they'll ask you more about specifics as it pertains to the art.
What's more important to tell the artists is what you expect them to do. Knowing about your idea is all well and good, but you need to say what's needed, with what kind of art style, the size of the assets, if you expect character animations and/or backgrounds, things like that. It's less time you're waiting for a response and less stressful for the artist trying to pull questions out of you.
It's important to know what you need to be done in your game and in what specifications because artists are not jack of all trades. There may be tasks they are not able to do, or can not do well, and you might need to use multiple artists to get what you want in the end. In addition, if you want to hire an artist early on because you don't know the art direction of the game, not all artists can act as directors. They too need guidance and do not inherently know what's best for your game. Only you can know that.
No, you don't actually have to talk about the strict numbers in the first conversation. Usually if you tell the artists the workload you have for them, they can give you a price or a per hour estimate. However, if you are not planning on paying the artist with direct monetary value you must tell them upfront. Waiting to pay until a kickstarter or doing revenue share are examples.
If you are offering the promise of exposure because your game will "make it big", just don't. If you game is really that great, it can make it just fine with placeholder assets. Don't ever expect anyone to do anything for your game for free or accuse them of not having enough passion. They are probably passionate about their own things, just not your specific idea.
Revenue-share is not impossible, but it's really shaky ground. You must have examples of previous games or programming experience, as well as extremely solid goals for your development.
If you really want to sell your game that you want the artist to work on, you should have some kind of experience. Many artists will take what's offered to them if you're paying, but it can be beneficial to both of you if your artist is convinced that this will be a successful venture. Required if doing rev-share or alternative payments.
Not a programmer? The programmer comes before the artist, and parts of the budget can apply to your programmer as well. Your game should really be already started before you bring an artist onboard.
It's not in the artist's best interest to tell you this, but if this is your first game, don't get art done. It doesn't matter if this is your passion project you've been dreaming about for years (there's a whole bit that could be said about what a bad idea that is), unless you like dumping money in a hole or your game is 80% complete, there's no reason for you to get assets done now. It will take time, your tastes will change, the style could change, it may be held up for years with your own inexperience, anything could happen.