The best way to have a good idea is to have lots of ideas.
A helpful quote for when you're stuck on that one great idea, trying to make it just perfect. Put it aside. Take a break. Make some tea (or eat some chocolate if you're lucky enough to be able to keep it in the house without eating it all in one fell swoop.) Relax. Then let yourself loose and crank out a bunch of others. Worry about sifting the good from the bad later.
Here's another article about generating ideas.