The beautiful game of poker should remain as fluid as possible, meaning few rules, but rules do help you introduce discipline into your game and one important rule to remember is never make a bet without a reason.
You Have The Best Hand
When you hold the best hand (or likely best hand) you are betting to extract money from an opponent holding a weaker hand. A good example is betting with ace-queen on a queen high flop against an opponent holding queen-ten. Keep an eye out for this at the World Series of poker 2012.
You Are Bluffing
When you do not have the best hand you may wish to bet to force your opponent to fold a better hand. In these sorts of instances you need to have a good understanding of the type of hand your opponent may have and the likelihood that they will indeed fold. It is also advisable to choose your bluffing hands wisely and you should always bluff with equity in your hand. A good example would be to bluff on a board of [9h] [7h] [Kc] holding [Ah] [Tc]. You have a back door flush draw and the added equity gives you the opportunity to double barrel bluff should your equity improve. So in the above example you can bet again if a third heart comes on the turn and your opponent may well lay down a hand as strong as pocket jacks. People with a Betfair Promo Code need to bear this in mind.
A third reason to bet is to take the dead money in the pot. Your hand could be ahead, but vulnerable to action on later streets, such as a pair of deuces, or you may have a strong hand like ace-king that has missed the flop but could improve on later streets.
Plenty of bets but each one for a specific reason.