Our ceramics instructor went around the group during the last class asking "where do you get your ideas?"
For these tiles, I'm having to come up with 15-20 different ideas, so I've gone to my idea book. As a class assignment a few years back we were to put together a book of ideas to use as a resource. Since then I clip patterns from magazines as I read them. (My own magazines, of course!) Those that catch my eye employ colors or shapes that appeal to me. Fabrics are especially good: the design flaws have already been worked out: I use them as jumping off points, utilizing some of their color combinations, or design concepts. I saw something like this on a summer sundress.
Another source for ideas is truly basic. Pick something you love, and go with that. I truly love quail. I think they are the neatest looking little birds. This is the first time I've tried to paint one. Not bad for a first effort, right?