When watching another aircraft that you're worried about, don't forget to keep looking for the one you haven't seen yet.
Know the speeds and RPM/MP settings for your aircraft - like, if S&L and you want a 500fpm descent, what power setting should you choose?
Never trust an ADF, especially at night, or near the coast.
Air Traffic Controllers are supremely friendly people (apart from one or two, but we all know who they are). They will help you immensely, if you but ask.
The first time you fail to check the drains, you will have water in the fuel.
Look carefully at the aircraft from a distance. Does it look right?