Here is a good article from North Sails describing technique for "how to improve your tacks". Really clear, actionable advice that can make a big difference in the upwind legs! Note the emphasis on managing heel of the boat before and after the tack.
If you are interested in tactics, here is another good article describing "tactics as you approach the starboard tack layline". This is a close encounter that occurs fairly frequently on the race course, and making the right decision allows you to stay ahead or get ahead. This article is written by Bill Gladstone (who delivered the weather and routing briefing for the Queen's Cup last Friday).
Lots of other good information in the North Sails website. Happy browsing!