Everyone has different theories on this, but here are a few things I look for...
-Unranked teams at home vs ranked teams are usually modivated and hit at a good rate
-Revenge games, in conference play you usually play each team twice so look and see what happened the first time. If it was a close game, and you're getting a line you feel comfortable with college students especially are modivated to win the second time around.
-Pick a few conferences you know well and watch to bet on... whether they're big conferences or small it's much easier to narrow the 100+ NCAAB teams down to a managable 20-30 that you know backwards and forwards.
- Prep time. Some teams get 5 or 6 days off between games to prepare for their next opponent, while some play games on back-to-back nights, obviously the more time you have to prepare the better your chances of covering the spread.
Luck is what happens when preparation meets opportunity.