Concept 1 - Don't 'gamble' early on the tourney.

What i mean by this is that you shouldn't go all in, or commit your chips on those hands where you believe you only have a marginal edge. This is because the best thing that can happen if you win is that you double up while the worst thing that can happen is that you bust out. If you bust out, you've lost your buy-in. But if you double up, you haven't guaranteed yourself of doubling your money.
Situations like this come up all the time in these internet tournaments, and you'll be doing yourself a huge favor if you learn to spot them. An example would be flopping top pair with a good but not great kicker when an opponent who has almost as many chips as you moves all in. As long as you still have most of your original chips left in front of you it's usually a good idea to get away from these hands and look for a better spot for your money.

Concept 2 - If you have a decent sized stack, and the blinds haven't yet escalated, don't be afraid to take flops with some marginal hands, especially in late position.

Remember in my Multi table article where i explained the super aggressive style of play (seeing alot of flops cheaply). Well, in the early stages of sit & go's this is where you can put it into practice as long as the blinds haven't gone above 15/30. Then you should be willing to take a few chances on trash and see what happens on the flop. Especially if you're on the button or in a late position. You can also try this if you have a large stack and the blinds are low compared to your stack. Just fold if you don't hit on the cheap flop with trash hands.

Concept 3 - Get aggressive in the middle stages of the tournament.

As the tournament progresses the size of the blinds begins to become significant. This means that it becomes essential to take some risks since you can't wait around for the nuts. As long as your stack is moderately sized you should be making more than your share of blind steal attempts. Of course you can't try this if someone else has already limped in, but so long as everyone has already folded, you shouldn't be afraid to take a shot at the blinds with some fairly weak hands. When the tournament gets into the middle and late stages most players make the mistake of folding too much in the blinds. When the tournament gets into the late stages this phenomenon no longer exists since you're usually down to four handed (or less) and everyone is on the lookout to blind steals. But in the middle stages most players are still dreaming of sneaking into the money which means they don't want to lock horns with crappy hands. Obviously you'll have to pattern your blind steal play after your opponents. If they're loose cannons you may have to watch out when trying to steal their blinds. However, the push overs will fold them to you in hopes that they can wait it out for other players to be knocked out so they can sneak into the cash. Stealing Blinds means when you catch a real hand they might call you more often if they think you're trying to steal and you can take them out straight away with your monster hand.

Once nice place to practice your Sit and Go Tournament game is at Fortune Poker, Paradise Poker and Pokerroom.com. These poker rooms offer a wider variety of buy ins and qualifiers. The competition varies, but is generally weaker at lower buy in levels at all online rooms.