I find that writing tests before writing the code to be tested helps to catch a lot of dumb mistakes. Also, writing a test for the obvious seems like a waste of time, but it may help preserve sanity in case of an acute attack of stupidity.

It also helps to consider refactoring the code (there's always something smelly) since it forces one to rethink the code. It ties in with the Extreme Programming paradigma which represents some nice ideas.

Just my 2 cents, -gjb-