Game theory and bluffing:

First you determine the chance that you have the best hand
Add that to the percentage of the time you will have the best hand at the river
Add the percentage chance your opponent will fold if you bet
Subtract the percentage chance that your opponent will raise if you bet
use that as your chance of bluffing

For example in the above $5/$10 NL game my opponent raises on the button to $30
I call in the BB with j/10 offsuit
the flop comes 389

I probably don't have the best hand, but I have an OESD with 2:1 chance of hitting, and 2 over cards
My opponent could have been trying to steal the blinds
so I will assume that there is a 10% chance that I have the best hand
and a 33% chance of having the best hand (not including the 6 outs from my over cards)
I think there is a 30% chance that my opponent will fold to my bet,
and a 10% chance that he will reraise (you have to gauge this on how your opponent has played up to this point)
so 10+33+30-10= 63%
so, I should actually bet this flop more than half the time.

You need also, however, to take into account the pot odds that your opponent is getting to call your bluff.
so, you take the pot size ($65) and consider your chances of making your hand (33%) then bet an amount where your odds from the pot- if your opponent calls- are equal to the odds of making your hand.

So, going back to the above example, I would bet the pot, hoping my opponent folds, but if he called, I would have bet $65 to win $130 (his call, plus the pot amount)

NOTE: This would not be a winning play, in general, except the amount of times that your opponent folds, more than makes up for the times you lose the hand.