The Two Move Triggers
Time management is very important in chess, and it is a topic that Dan Heisman discusses frequently in his Novice Nook articles. One article that I particularly enjoyed is titled "The Two Move Triggers". His latest article "The Room Full of Grandmasters" also touches on this subject.
The 2 move triggers are:
1. You have proven which move is best, so no further time is necessary
2. You have not proven which move is best, but time constraints make it efficient for you to play the best move you have found so far.
You can find Dan's Novice Nook articles at chesscafe.com and he also has some nice indexes of them on his own website at danheisman.com