Have fun and don't stress!
Learn and practice your dive tables - I think everyone needs to understand what their dive computer is telling them - and be prepared to deal with a situation where the computer is broken, lost, dead battery etc.
And then practice, practice, practice those underwater skills. Clearing anything (mask, ears, reg etc) should be second nature and almost a habit. Practice brings understanding and comfort - which makes all of your dives much more enjoyable and better prepares you to work through any challenges or out of the ordinary situations that may arise.