Hi Rushino. Just wanted to chime in here, as I've spent a good portion of the last year studying Greenlight and the Steam market in general. I've submitted three concepts there, with varying degrees of success (15%, 30%, and 95%) and have a fair bit of insight here as a result. Be ready to change your game, as well--- if you've got a lot of time invested in a particular concept that isn't well received, it could be extremely discouraging. It's up to you to decide who your audience is, at the end of the day--- if you're a Steam gamer (or multiplatform veteran, for example) then that's probably who you'll be targeting. If you're a casual gamer, stick with mobile or Facebook games. Your best work will be where your past experience meets the crossroads of your personal strengths. There are just too many other people out there making great games about what *they* are good at--- I spend a lot of time explaining this to people I meet in person (because everyone has a great game idea, of course...)
The best advice I can pass along is this:
Make the game that you want to play that no one has made yet. This is *by far* the most important thing in the long run. Every element may have already existed in other games over the years, but if it smells like a clone of something else currently available (read also: everything ever made), the voters will tear it to shreds.
For Greenlight specifically, follow these steps: Polish your prototype. After that, polish it more. Then a few more times, for good measure. If it doesn't look good, it doesn't matter how great the rest is--- seriously. For some reason, Steam gamers seem to favor good graphics over literally ever other aspect of a game when it's in the Greenlight stage. If you look at the titles that are passing through Greenlight, they only have one thing in common, so far as I can tell--- polished graphics. If the gameplay sucks, it may pass Greenlight but at that point, the scrutiny will shift to gameplay, features, and setting/genre elements.
Hope this helps!
Cheers.