There are several lists of Mathematica tips on the web, such as example1 . I have tried to avoid duplicating the efforts of others, but obviously there may be some overlap with other lists. I have also included a list of bugs that I have encountered.
Just because I have mentioned bugs and some tricky issues in this list should not be taken as a criticism of Mathematica. I think Mathematica is a splendid product (otherwise I would not wish to work with it) and all large pieces of software have at least a few bugs!