The two main elements are pot odds and equity against the opponents range (maybe?)

1. A call can be +EV in two ways or a combination of the two.
a. If the amount to call as a percentage of the pot is less than your equity against the opponents expected range then a call is profitable.
b. If the amount to call as a percentage of the pot is less than the percentage chance of you improving

2. A value bet or raise is +EV if if offers incorrect drawing odds to your opponent, or if it is greater than the value of their expected range equity.

3. A bluff bet is +EV if it forces the opponent to fold a greater percentage of times than the percentage of the pot the bet represents. A bluff bet is also +EV if it forces the opponent to fold at a value less than their expected range equity against your hand.

That's my shot at it. Extra credit?