There really isnt a correct frequency to bluffing. Its all dependant on the reads you have on the players around you. If you think you can get a lot of bluffs through to steal pots, then do it. If however the table is quite loose and call with a wide range then you should not bluff as much.
I guess if you keep getting caught bluffing then you are doing it too much. If you never get caught you arent bluffing enough.
Also it can be a good thing to get caught bluffing in certain situations as it can set you up to win a big pot later on when you make a similar move but this time with a monster.
Position is also key. If you are out of position then bluffing is a bad idea. If you are in good position such as on the button, you can pretty much play any two cards you like.