If you are really serious about playing in a Sit n Goes tournament then you should seriously consider visiting a poker website which offers mentoring and coaching to players. There are several such sites that you can be find on line and which will provide you with SNG strategy tips and hints in order to help improve your game.
One reason for using a mentor is that they will actually ghost your tournament play and help you with any strategy along the way. So as you play a tournament you will be on the phone with your mentor and they will watch the tournament table. You will tell them what cards you have and then you will discuss what strategy you are going to use together. The reason why this method is much more helpful than any book advice is it is real time and also highly practical for you whilst you are playing.
Whilst playing the first 3 to 4 levels of a game you should play a fairly tight strategy and only play the good cards in an early position. Then play some more speculative hands in a later position where you can see a cheap flop (suited connectors or small pairs).
Then as you progress from the early stages in to the middle stages of a tournament you should start to play a little more aggressively with lesser hands.
Finally as you get into the late stages of a tournament you should now start to get very aggressive in the way you play. It is important that you make sure you play aggressively on the bubble especially if you have shorter stack than your opponents.
If you happen to notice a player during a game who is playing fairly tight and is not taking many chances until they are actually in the money then watch what they are doing. Make sure that you think about what they may be holding before you decide to commit a lot of your chips against them.
However the best SNG strategy to use if you are just trying to make money is to play very tight throughout the tournament. In most of the tournaments that you enter you will find you get enough hands early on to give you a good stack of chips which will last you. Then once you are close to the money then loosen up your game.