AN attempt at over simplification is figure out how many "outs" you think you have. Divide the number of unseen cards by the number of outs. To get implied odds you have to subtract the number of cards to come from the number of unseen cards and then divide by the number of outs. This is as simple as I know how to put it. In limit you then compare how many more bets you think it will take to get to the showdown to figure out how you should play the hand. That is why NL is so much more profitable for players who know how to bet they kill their opponents odds so if the guy chases a flush draw, even if he hits it against you the bet you made had positive expectation. Simply you will win more of those than you lose and that is where you make your money. I just reread your post your wanting to know basically when it is appropriate to chase a backdoor straigh flush or what not, not much more complicated really the way I do it is if I need 2 exact cards I firgure 1 out for each card to come so the turn in hold'em would be 47:1 and the river would be 46:1. River assumes you hit one of your cards. That is how I do it anyway!