Short-handed GAMES

Shorthanded games give the aggressive player the edge, if they know how to play well. However, just because shorthanded games require aggression, doesn't mean you should become loose and aggressive. Those players take massive swings at shorthanded play, and inevitably end up losing in the long run.

Before you should consider tackling 6max, you should be very competent at the full ring game, with enough hands to know you're soundly beating the game. There are many things profitable in full ring that go down in value for 6max. For example, suited aces are very profitable full ring in a passive table, because with such a big pot with dead money, it's worth chasing for that flush. In 6max this will get you burned.
In this guide, you are learning to be tight and aggressive. It’s the only way to play. By tight, I mean you should be seeing 20% of all flops out of the blinds. Unlike full ring, if you see lower than 20% you are missing out on a lot of profitable situations, and that will affect your win rate. When you get enough experience, you can move up to 25% of all flops. 30% is the highest you can play profitably at, and very few players can achieve that.

Also, if you plan to play seriously I highly recommend Poker Tracker. For limit it is essential to analyzing your game, and plugging leaks. Limit is all about the little things. The player with the least little mistakes makes that extra 0.5bb/100.
So I’ve mentioned playing aggressive, mentioned playing tight, and there's one last thing that's very important, in fact the most important. POSITION. Having that button is so crucial that your starting hand requirements change drastically relative to your position from the button.
Now that you have a general idea of what 6max is all about, time to break it down.

Position is the single most important deciding factor of what hands to play, so I’m going to break it down by position. Under The Gun:
Open raise or fold. You do not want to call here with anything. The only exception is if the table is unusually aggressive preflop, and you hold AA or KK, and you know there's an 80% chance there's a raise behind you, then you can consider limp-raising. UTG is the worst position preflop, limping can be very costly if someone raises after you. You must open raise to try and get as many people to fold after you, or try and induce mistakes by making them cold call.
As a side note now that I mentioned, cold calling is a HUGE leak in many people's games. This goes in full ring, and it applies in 6max. Do not cold call! Exceptions are if you're on the button and 2 people cold called already, and you hold a suited ace, expecting the blinds to call, etc.

Under The Gun +1 Again the situation is very similar to UTG.
Cutoff: This is when you start to get good position. The only time you should call is when UTG or UTG+1 limped ahead of you. Otherwise, if you're going to play the hand, raise. You want to buy the button by making them fold.
Button: Again, like CO, call only when there are limpers before you. If it's folded to you, raise with decent hands if you think there's a good chance the blinds will fold.

Now, I mentioned calling only against limpers. The decision to call vs. raise is often very close. For example, I call with KTo, but I’ll raise with KTs. Don’t get too stuck up on things like this, your decision preflop in situations like this account for a small percentage of your win rate over the long run. Postflop is where all the money is made.