The captions should be self-contained. Imagine that the reader has only the captioned figures and tables to figure out what you have done. Labels (words as opposed to `I' or `x3') on the figures can be very helpful.
Symbols should be chosen carefully. Redefinition of symbols should be avoided at all costs (such as X, X' and tilde X -- all being variants of the same quantity). Again a table of important symbols with the defining equation or at least its equation number could be useful.