A rough rule (from economics) is that you should bluff until the money you lose from getting caught approximates the money that you would forego from not bluffing. That is, you should equate the "marginal utilities" of the two activities.
If you "never" get caught, you aren't bluffing enough. That is, you are leaving money on the table with a number of bluffs that you could have "run" but didn't. You SHOULD get caught, partly for "advertising" purposes, and partly so that you "start" to lose money bluffing. Then bluff "a little more" and stop when you lose a little more. If you get caught "too often," you are losing more money than you're making with your last few or "marginal" bluffs.