Speed, time, and distance. Current, set, and drift. All these terms should have meaning for you. It's best to use several means of determining your position whenever you can. 2-hour watches if there are just two of you on board.
Autonomy is also important.
All watch-standers should have decision making authority. They should be allowed, even encouraged, to make certain decisions. If they are not, then you are doing something wrong. All on board should ideally be able to handle the boat if necessary. Have an emergency plan and practice it.