My lord this is a broad question. There are so many variables involved w every bluff in every different game. My main game is No limit holdem so i will give some tips just for that game and the various variables involved in each bluff situation. First off, your chip stack is going to matter a great deal in your bluff as well as your opponent(s) chip stack(s). If you are trying to bluff someone who is a low stack when blinds are high there isnt much chance of you getting away with it because they may already be pot committed. Secondly, if you have a low stack and are trying to bluff someone with a higher chip stack chances are they may just call you down to find out some information and are not scared of losing chips because they have more to play around with. Now that is just in tournament poker, so lets stick w that for a minute. Next, the way the hand is being played out is going to give you the best chance for a well played bluff. If you are betting straight out into a flush draw board, (i.e. 2 of the same suit on the flop) chances are people arent going to believe you when you try to represent that bluff. Now if you want to represent a bluff you may have to figure out how the hand is being played with the respected players in the hand. For example, are they checking on the flop w the flush draw? Are they trying to represent top pair on the flop? Did they raise preflop? all of the because factors when you are trying to represent a good bluff. Your best chance for a good bluff is going to represent itself when you can find a little bit of weakness from your opponent. First off, do not try to bluff in multiple player situations because chances are somebody made a hand or actually has the hand you are trying to represent, so try to be in isolation when making a bluff. If representing a flush for a bluff you are going to want to put yourself in the situation of how you would play this if you actually hand the hand. So like I said, they wont believe you if you are straight betting into a flush draw board. If you check call on the flop though, and you have an equal stack with your opponent, when the blinds arent too high relative to your chip stack you will have a good chance of getting away with a bluff. if you are in position or out of position has a great deal to do with it as well. So you are going to want to put yourself in that situation, how would you play the hand if you actually had it. Make sure that you try to trap if you are representing a flush, which btw is probably the easiest bluff to pull off. Now if you are trying to reprsent top pair right off the flop, think about what position you are in and what the top pair on the board is, if it is an ace you are going to have to of raised preflop most likely to represent the ace and get away w the bluff, maybe even a king, But if the top pair on the board is a 10 or an 8 you are going to want to have called a preflop raise or be out of position when you go to represent it. Now representation of a top pair on board is nearly a 2/3 or 2/5 pot size bet on the flop, so something like that would be your best chance of pulling off a bluff. If the opponent calls the flop though it make take more than one barrell to get them to fold. You will have to see if any over cards have hit the turn, but another solid 2/3 or even 3/4 pot size bet at this time is your best chance. If you get called a second time you may want to lay off because chances are the bluff isnt going to work unless you can put your opponent on a flush or straight draw, and if that is the case you are going to have to be aware of the river card and if it has compeleted any draws. If it looks like all draws missed and you are still ok w your top pair (or represnetation of top pair in this case) then you will want to bet again, however I would not continue to bet the same size fraction as the flop and turn becasue that is not how you would play the top pair. Instead make a value river bet becasue if they are on a draw they will have to fold anyways and if they actually hit an inside draw or something crazy that you havent seen then you will actually be saving chips. Now these are just some tips on bluffing a top pair and a flush draw in a NL holdem tournament situation. There are plenty more tips that can be given but obviously i have no time to write an entire book on this subject. Good luck with your future bluffs.