Inspiration
One of the most difficult parts of painting is getting the inspiration for your project. Once you figure out what it is you want to paint, the paint can just flow. If you're new to painting, and just don't know where to start, this link can be very helpful to get some ideas flowing for you: Things to Paint for Beginners.
If you enjoy painting, but just can't decide what to do next, these Painting Exercises can help you figure out some great ideas. If you paint regularly, but find yourself in a rut, try looking over these helpful Inspiration Tips for Artists to get yourself back into the painting groove.
True Story
Many professional painters get into ruts and find excuses as to why they aren't able to think of ideas like the artist who wrote this article. She explained that she found herself unable to just paint for the fun of it anymore, so she tried a simple trick to get her back to doing it for fun: doodling. She got her sketchbook and just drew without caring about the outcome, and that helped her creativity flow.