Rule of Four

If you can find a move that does one of these things, then that is good, if you can find a move that does more than one, then that is very good:

Rule 1. Strengthen your own groups.
Rule 2. Weaken your opponent's groups.
Rule 3. Expand/strengthen your territory.
Rule 4. Reduce/weaken your opponent's territory.

(As told to me by T-Mark Hall). I heard this from someone else in a different form: Priority is decided by:

1. Making your weak groups strong.
2. Weakening your opponent's groups.
3. Playing "big points".
4. Preventing your opponent from playing "big points".