Usually you are making a bet which you want to be confirmed by your poker opponents, whenever do you have a better hand than he has and you want him to pay it off. In cases like this one of the main rules you should follow is to do exactly the opposite of your actions needed when you bet with the single purpose to make your opponent to fold.
You should bet with the maximum which you think will make the man against you to call. In such case is advised to make a few bigger but rare bets instead of betting with smaller sums frequently. For this purpose you should know your opponents better and to decide when and if they are willing to bet and with what money.
Some players think that the higher bets are bluff, but the rest may decide that you have a strong hand to bet with so many. Both strategies could be tested and applied at few online poker games.
You should always be careful and to use the valuable information you collect during your poker game. This way you may decide at any point what size of your bet will give you the highest revenues.