When I found this place I could not post fast enough. Over the years I've hit a brick wall or 2 or 3 times BUT, I crawl back every time. No matter what your hang-up is, as long as you have a library card, as you will see, YOU CAN POST!
Step 1: Idea
The best ideas, I think, are our day to day habits..... the little things. Every one of us does things differently. Even just showing your version of how you deal with your tooth paste tube makes the cut.
Surf around instructables. Personally, if I surf around instructables and don't come up with an idea, I turn off the computer. This place is full of great stuff to do AND improve on.
Ask or talk a subject up. Get into some of the forums and chat away. You can also post in answers for things you are working on.
Furthermore, read the comments below. I know people will put up some more great ideas.
Step 2: Get a Plan Together
I actually use paper for this. Just scribble some steps down and let it flow from there. Ideas grow as you go!