Most people will tell you to keep a journal of all the ideas you have, and that's good, but don't forget all the other things!
1) Journal problems
2) Journal solutions
3) Journal possible names
4) Journal words that "roll of the tip of your tongue"
5) Journal characteristics of a possible character
Always remember to move your written "notes" onto your computer. You should do this because you can't lose something virtual. Email yourself the ideas you've come up with, or simply save them as a Word Document.