Bluffing Ratio

[Brad22]

When you're playing NL MTTs, live or online, do you have a certain bluffing ratio that you are using? For example, depending on the table you're playing at, do you have some determined amount of times where and when you are going to bluff a hand, either pre-flop or after, or is everything really based upon the player and the flop/situation?

How often are you using tells to make bluffs, rather than simply using randomized bluffs where you sense weakness? (In the case where you're not hitting flops, getting good cards, or need chips to have a chance)