The problem with this question is the answer is different for everyone. In general, however, avoid eating dairy (it is mucus forming and feeds inflammation), avoid sugar (also feeds inflammation), and try not to eat processed or deep fried foods. You will also discover your specific trigger foods. For example, I can't eat soy, animal protein, or grapes. I know someone who can't have tomatoes. You're going to have to pay close attention to the food/pain correlation. I recommend starting an elimination diet. Pick a food (or food group - dairy, gluten), stop consuming it, and keep a journal of changes you notice in your pain and energy levels.
If you have a sweet tooth like me, check out the web site Chocolate Covered Katie. She has quite a few treats sweetened with alternatives to sugar. A couple of other great sites for recipes are The Minimalist Baker and Forks Over Knives. Changing your eating habits can be overwhelming. It helps to have places to turn for snack and meal ideas.
Making dietary changes is the single most effective thing I have done to manage my pain.