Betting after the flop
There will be varying opinions on how to bet on the flop, but I believe the best approach is a consistent one. What I mean by that is to make the same type of bet every time you are leading the action. The amount doesn't matter as much as the fact that you are consistent, although it is probably better to use a smaller amount of a half to 2/3 the size of the pot than to bet the size of the pot.
A smaller bet of half to 2/3 the pot size will allow you to fold those hands when you get re-raised but is also a large enough bet that you will get respect. It's also a small enough bet that it's an action generator, meaning that people will continually test you by calling you down or raising you in improper situations (when you have the best of it).
But this does not mean you should always bet this amount. Certain situations will warrant making a different bet amount. For example, say you see a flop with an opponent and a half pot bet would be 40% of your opponent's stack. You know that you will not fold if he moves all-in over the top of a half pot bet, so rather than leaving yourself with a decision you move all-in and put the pressure on him. In that type of situation, it's perfectly acceptable to bet something other than your standard bet.
How much to re-raise
When it comes to re-raising a player, how much you bet will depend primarily on how deep your stack is. If you have plenty of chips behind you, then you should be making a raise that will best accomplish your objectives. If you want a call, you want to raise the maximum possible for that particular opponent that you believe they will call. If you don't want a call, you want to raise the minimum possible that you feel they will fold to.
I still think a standard amount works best in these instances because you are then able to bluff raise and value raise without giving your opponent any information. When you start varying your raise amounts you always have the potential for giving your opponents information about your hand. What amount you raise is up to you, but I typically raise two times their bet amount. So if they bet 1,000 into a 2,000 pot, I will raise it 2,000 to make it 3,000 to go.
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