As You enter the Middle Stage of a Sit and Go Tournament, some players will have been eliminated and the blinds will have increased to the point where they are a greater portion of your total stack. Sitting around at this stage of the tournament is a strategic mistake and you have to start to be more aggressive and get yourself in a position where you can go on to win this SNG.
As two to three players are eliminated, and the blinds are increasing, play starts to become more aggressive.
Seeing flops with low pairs and suited connectors is no longer profitable, because the implied odds of hitting a big hand are reduced, and the ability to draw to improve is almost gone.
Since the table is short handed, waiting for good hands (or taking flops with mediocre ones) means you're going to be one of the shorter stacks, not one of the larger. Ideally, you want to get to the bubble stage (four players left) with 4,000 or so chips.
Since you will probably go around the table three times while playing down from six to four players, the blinds alone will knock your 2,300 average stack down to 1,400. That won't work, so you must do one of three things.
Get a bad preflop call from another player when you raise with a good hand.
Blind steals are fairly important at this stage. If you were fairly passive in the early stages, not raising the players on your immediate left too much (without big hands, anyway), your raises at this level will get a little more respect.
If you raise with any two cards from the button, standard ABC players will likely only defend their blinds about 20% of the time (and only a few of those will be reraises).
That means your steal raise has a 64% chance of success from the start. You can reasonably expect to get in one or two successful steals at this level and remember that each time you steal successfully then that covers the cost of the blinds for one whole circuit of the table which buys you more time to wait for a good hand to play.
All in on a coin flip means taking a hand that is either a pocket pair or two big cards (preferably Ace Ten or better), and reraising all in against someone that previously raised the pot.
For reference, most pairs are slight favourites against two big cards (8-8 is a slight favourite over A-K) when both are all in before the flop. Yes, it is possible that you will go all in with 8-8 and get called by J-J, but again, that's being afraid of monsters under the bed. You must take these calculated risks at times to be a long term winner.
You raise with a premium hand, and another player makes the mistake of calling. Even worse for them is if they actually hit part of the flop but with your hand still in the lead.
By the way, you cannot lay down premium pairs here. You do not have a stack deep enough to determine if someone got a lucky flop on you. True, you can lay down J-J if someone bets into you on an A-K-Q flop but in general with premium pairs at this stage of the tournament you are either going looking to double up or get knocked out and move onto your next SNG.
Your prime objective for the middle stage of a Sit and Go is to survive through to the Bubble Stage (4 players left) with 4,000+ chips in your stack.