I can tell you what i do but I am no professional by any means.
If there is more than one other player in the pot with me I have to decide who is bluffable and who is a calling station. A calling station will call no matter how bad his or her hand is so you have to be careful with calling stations.
First thing is I always tend to raise if I am in late position and no one has raised before me; if i see a few people fold, then I consider that raise a success because I just lowered the probability that they will "suck out" on me (which is to say, draw out on a hand that preflop was inferior to mine).
You can call that a bluff or not but its really something I try to do as often as possible. But of course, if you do anything too often, savvy players that have been watching you the whole time may try to set you up and trap you by slow playing something big in anticipation of your raise. This is why when I do raise, I don't raise an amount that would cripple my chipstack. In general, when raising because no one else raised, my raise will be about 2.5BB. And of course, will only call a big reraise if I actually have something....my definition of having something changes depending on the range of hands a particular opponent could have (i base this decision on stats I have obtained about the player during the game so far).
As far as bluffing on the flop, turn, or river, I will tend to do this when I am on a draw of some sort or if I have 2nd top pair. But this is largely villain-dependent as well. I will be looser with aggressive-tight players in my bluff and tighter with loose-aggressive players in my bluff. If I am up against a calling-station, I just play straight up poker: i don't try to bluff someone like that. If I am at a table with a bunch of players who I know are bluffable and just a single calling station is still in the hand, I don't even try to bluff.....
I think bluffing is more about knowing what you can get away with and with whom. Some people are easily bluffed over and over and over and over again. Others, just once in a while. Yet others will always call your bluff. So the game I try to play with the latter type of player is to raise really big against such players when i have something; and if i keep doing this with calling-stations i look for the point at which they no longer call my bets. When I see that calling-stations are deliberately not calling my bet anymore, I can start to bluff them...but I always do so with caution because in my mind, ONCE A CALLING-STATION, ALWAYS A CALLING-STATION AT HEART...
allin at flop. when i saw my opponents hand i close my notebook :S
