Short-handed Strategy

Early Position: If you've been betting the entire time, you should bet again if the river is a blank. If the river completes many potential draws, you should still bet it. Just because the river card completes flushes and straight draws doesn't mean your opponents hold them. If they are straightforward opponents, they might raise you, allowing you to fold (only if the pot is under 10bb, call if it's big). You spend just as much when you are ahead as you are behind. Check calling the river automatically when a scare card comes will make you miss a lot of value bets. Do not assume the worse. If they shown a lot of aggression on the turn, then I may check call it down.

Middle Position: If you're still at the river at middle position, you must have a pretty good hand. If someone early bets, before you call rerun the hand and see what late position players have done in previous streets. You do not want them raising after you because it will be very costly.

Late Position: Call down scary rivers in big pots. Bet blanks when you have a hand.
Facing a raise: Again, most players will not raise back at you without a good hand on the river. However, before you go psycho and hit the raise button again, put them on a hand. Just today I was dealt rockets. Hit a set on the flop, bet the flop, bet the turn, bet the river, and I got raised. I paused for a second, and I thought no fricken way they have QT for the gutshot on the river. I reraised, and they cap it back. Yep they had QT.

Bet or check behind? Bet out, or check/fold?

Theory of Poker mentions that sometimes you cannot bet because the only hands that will call are the ones that beat you. This is true, but only with thinking opponents. Loose low limit games are filled with players who will call with the lowest pair just to make sure you aren't bluffing them out of the pot with an unimproved AK. Because of this, you should be able to value bet a large percentage of your hands, even the marginal ones. Put a label of tight or loose on the player and adjust accordingly. Tend to be aggressive against loose opponents, and passive against tight players on the river, with your marginal holdings.

A lot of this information is explained in greater detail in Ed Miller's Small Stakes Holdem. It is an excellent book and I recommend it to anyone who wants to excel their holdem game. However, do not follow his preflop charts in shorthanded games for which hands to call. Limping is a money loser shorthanded, don't do it first in the pot. Raise if you want to play the hand.

Now, an important concept: PROTECTING YOUR HAND

The concept of protecting your hand is trying to make your opponents fold better hands, or make them call unprofitably. Many limit players from the full ring get slaughtered in shorthanded games because they fold too damn much! The fit-or-fold strategy in full ring is a sure money loser shorthanded. They hit top pair, but weak kicker. They will fold sometimes even for one bet on the flop, because the thought of being outkicked is so menacing. They don't know they are folding the best hand more often than not.

So, bet and make those players fold! Now, what about someone early betting, and you raising with mid pair good kicker after they bet? This gives these weak tight players even MORE reason to fold their top pair weak kicker because it costs them 2 bets. Remember, you want overcalls if you're drawing to a monster, or flopped a monster (like a set). You only need to raise to protect weaker one pair hands. Many loose players call, even to the river with low pair. With each additional caller, the one after is getting better odds to call. You want to raise because by making these players fold it improves your winning chances (for the times the turn and river makes their hand into the winner).

People might argue that if you don't raise the flop, you are going to miss bets with the current best hand. This is often wrong. Players will tend to check/call down players who were aggressive the previous street. "Check to the raiser" is very common in low stakes games. That's why freecards, cheap showdowns, free showdowns, etc. work. Because of this, if you raise the flop, you will only get them to call your turn and river bets. If you just call the flop, but raise the turn, since you are now the new aggressor you get at least one extra big bet.

There is an interesting concept when you are playing against multiple bad players, them COMBINED can have enough outs to beat you. So instead of the 1st player having 4 outs, the 2nd player 4 outs, 3rd player 4 outs, you can think of it has 12 outs against you. This is called the "schooling" concept. You should raise to slim it down to 8 or 4 outs against you.

Another reason for betting and raising, is because players tend to check to the raiser of the previous street. By betting and raising you can take free cards and free showdowns.

WHEN RAISING WILL NOT PROTECT YOUR HAND

Even though you can protect your hand by betting and raising, sometimes you are unable to protect your hand. For example, preflop UTG limps (bad! don't do it yourself), and UTG+1 raises. CO folds, and you 3bet your aces. The small blind folds, big blind calls (bad yet again), and the limper calls (bad!). The big blind and limper have done terrible mistakes by cold calling. Be happy if they are doing it all the time because their money will end up in your pockets. Anyways, on with the hand...UTG+1 caps, and everyone calls.

The pot is 16 small bets. There are very few hands that will cap preflop, so you can put UTG+1 on KK or QQ, etc. The flop comes with a 2 flush, and 2 to a straight, medium cards. You almost certainly have the best hand, however, your hand is vulnerable so you should protect it. You probably have UTG+1 beat unless the miracle K or Q comes, so your concern is the blind and limper on a draw. The small blind checks, limper checks, and UTG+1 bets again. You should NOT raise.

Why? Playing poker is all about inducing mistakes from your opponents. There are people that argue that the chances of you having the best hand are TOO great right now, so you must raise for value. However, after you raise, the pot will contain 19 small bets. After your raise, the SB gets 8:1 odds to call, which is the treshold to call profitably for 4 out draws (because of implied odds). The limper gets 10.5:1 odds after the blind calls. And with one bet back, UTG+1 can even call a 2 out draw profitably! Since you shown aggression on the flop, your opponents will likely check to you on the turn. But since you raised it on the flop, on the turn the pot will be 12 big bets. So even if you bet, any 4 out draw (like gutshots) can call profitably getting over 12:1 odds. Thus, in this situation raising the flop will not protect your hand because your opponents can call profitably (and with the pot so big you can be CERTAIN none of them will fold). Your raise does not make your opponents do any mistakes.

Your best chance to protect your hand is to wait for the turn where the bets double, and the turn doesn't help any draws. If you called, the pot on the turn will be 10 big bets. The small blind and limper haven't done much except call, so you can expect them to check to the raiser UTG+1, who will bet, allowing you to raise. Your raise will face the blind and limper with 13:2, or 6.5:1 odds, which is far too crappy for one more card to come. You have just allowed your opponents to make mistakes by calling, thus you gain.

People still argue that they want to win the biggest pot possible by raising the flop and then planning to raise the turn again. However, because the theme "check to the raiser" is so common, you will actually more likely make the pot SMALLER by raising on the flop instead of the turn. Reraising the flop will slow you opponents down on the turn (unless they themselves have a monster). But just calling the flop, and unexpectedly raising the turn will tap them for at least one more big bet, resulting in a bigger pot.

In summary, a flop raise fails to protect your hand when the raise allows your opponents to call profitably (ie big pots). Wait until the turn. With one card left on the river to destroy your hand you are less likely to be taken down. Jam the pot on the turn, and charge the callers more than what they bargained for.

Your opponents' mistakes is money in your pocket. Do whatever you must to make them do the MOST mistakes.

POT SIZE & OPPONENTS: Now before you go raising everything, you need to look at the pot. ALL decisions should be centered on the size of the pot. If the pot is 3 small bets, and someone bets and you hold mid pair good kicker, it's not worth spending 2 small bets to win 4. So fold it.
However, if you have a marginal hand, with a backdoor flush draw, you have some outs to the best hand (such as trips on the turn, 2 pair, flush redraw). If you have the odds (and/or implied odds) to call, THEN that's when you want to raise, to thin the field.

With weaker hands such as single pair, and sometimes 2 pair, you want to thin the field. With flush and straight draws, you want many opponents. Many players make the mistake of betting and raising the crap out of their straights and flushes when they hit on the turn. What they don't realize is they just make it heads up, instead of gaining the 2 extra bets from callers if they didn't raise. Maximize your hand! Straights and flushes are strong enough to take down many opponents, so keep them in and take more of their money.
Fine print: Just as a warning, playing marginal hands is a HUGE money loser if you do it wrong, so before you raise that mid pair or even bottom pair, ask yourself why you are raising, and what you want your opponents to do when you raise. But of course, if you don't play marginal hands at all shorthanded you'll get your ass kicked anyways. So learn to do it well!

Also, this entire post about protecting your hand is from the material I learned in Theory of Poker and Small Stakes Holdem, so props to the 2+2 authors who awakened me when I first read this.

THE SWINGS: I'm sure most of you have heard of the 300BB rule for full ring. And if you haven't you probably shouldn't be reading this guide. 300BB is the MINIMUM you should have for 6max. Don't even think about playing shorthanded without being properly bankrolled. I've taken 40BB swings up and down playing shorthanded within an hour or 2 (I've heard of people taking 100BB swings as well). Since you're playing many more marginal hands than normal, you'll be going to showdowns thinking you'll only win 60% of the time. Full ring, often you shouldn't go to showdown without being 80% sure you'll win. This amounts to way more swings than usual. Not being properly bankrolled is just asking the poker gods to bust you.
Anyways, on to more strategies.