Just last night I was reading about some ki excercise (for Xing Pi or something like that). Train at sunrise, midday and sunset. Do not train when the stomach is too full (or you will injure yourself) or when too empty. Don't eat, drink, defecate or urinate directly after practise (as it results in a loss of ki).
Don't know much about the truth of this myself - generally I have to drink after pretty much any excercise!