Although it may not work in every single cases, but one can find numerous game making contests on the internet with different topics, criteria, etc. I personally find them quite motivating, since they are mostly about small projects, have a prize, and most importantly, have a deadline, which makes me work on the game day and night
So the main point is, try to find a goal, sort of a deadline for your project, and you're more likely to finish it. I think after making the first game and getting some positive reactions on it -friends will surely give positive reactions on a self-made game-, everything gets easier and one can already have all the motivation needed.
For ideas, you may want to look around on the forums, I guess ideas are the easiest to find (since most people everywhere just have brilliant ideas... or ideas they consider brilliant), while graphics are the hardest. So I agree with Reneuend that graphics should be kept simple. If you don't want to use photos, you may want to look at some basic drawing tutorials; those together with free textures, images from the net can make wonders!