Clear & copious. Drink tea in tea season; avoid coffee, and you should already be done drinking sodas.
Hydration is pretty essential.
Beyond that, my most productive strategy was not to eat past 8pm. Similarly, consider becoming vegetarian or vegan.
As a means of explaining food & digestion & basic strategies, this was very helpful & formative:
http://www.fourmilab.ch/hackdiet/www/hackdiet.html