I second that. As you start flying you will learn what routes you want to upgrade. When I was PLT, I generally upgraded MIA flights from NYC because they tended to be completely full (no open middle seat.) Also, a mainline flight like TPA/MIA or DFW/AUS is not worth upgrading unless you have a huge stock of stickers.

Funny story about a year ago I was waiting for my LGA/MIA flight. At the gate next to me a GA was asking a PLT why he did not want to use two of his 68 stickers to upgrade on an ORD flight. The gentleman told the GA that he saw no difference between coach and first and had no desire to upgrade.