I almost dont play 6 max ring, but I will take a shut at your questions.

First thing first - when you bluff you have to bet like you mean it. It has to look exactly the same as the way you bet your hand. Bluffing halfheartdly is one of the worst things you can do because any decent player will spot it and come over the top with any two.

How often do you bluff - As often as you can get away with it. As with everything in poker - it depends - in this case it highly depends on the table fabric (loose, tight, calling stations). It also depends on whether the other players play their cards or play situational poker.
For starters dont bluff in a multiway pot, you can get away with bluffing one or two people, but not three or more.

A bluff usually has to be consistant - The easiest bluff to pull is continuation bet - you show strength preflop and you show strength on the flop.

'Bluff' is actually taking advantage of a situation, for example if you think your opponent is drawing then you can 'bluff' them if the draw does not hit with any 2.

Another good type of bluff is the check-raise bluff. This requires a bit more reading skill - you have to put your opponent on a continuation bet and come over the top

How do yu calculate how much to throw out on a bluff - This is actually the easiest question to answer - bluffs has to be in line with you normal gaming. In a bluff you try to represnet a hand, so bet like the hand you represnt. If you usually bet pot size when you have TPTK then bet pot size when you want to represnet TPTK.

How to bluff and keep your game intransparent - as I said, a bluff has to look like a decent hand. If you are playing with decent players you cant pull too many bluffs with out getting challanged, if you play with villian who only play by his cards you can bluff him out of most pots.