Well, the only tip I can give you is: Don't underestimate. You may have this over-ambitious idea in your head (we all do), and I can tell you right off the bat: it's not realistically implementable.
Also note that the time in this parallel universe of programming runs about 8-9 times faster than real time, which means in reality you only have a little less than 4 days to make this game.
With that said, I recommend you note down a few veeery simple concepts. Things that are so stupidly easy, that you will be able to program them within a week. Here are some ideas to start with.
- Walk around on a terrain in first person view
- Generate a 2-dimensional maze
- Have a character jump and move around in third person view
- Program a space ship to move around in 2-dimensional space using the arrow keys (much like the classic game "Asteroids")
Great games always start with simple concepts. If you can get one of the above (or your own) running, then you've successfully taken the first step to making a game. You have a framework which you can expand on, breath life into, give a meaning.
What you make is entirely up to you. I know from experience that FPS, 2D shooters, and generally 2D games are quite easy to make, where as RTS, RPG, MMORPGFPSGIGAFIFA and sports games are incredibly retarded and prone to errors.
TheComet