So you've made it through the early stages of a tournament and are trying to decide if you should shift gears now and put the pedal to the medal or just ease off the gas.

Let's answer this question from a chip stack perspective.

Let's say you are entering the middle stages with a small stack.  In fact you are the short stack.  As the blinds are now starting to become more of a consideration for players I usually like to be a little more aggressive at this stage.  I would definitely expand my range of playable hands and would be pushing not raising.

Besides the premium hands I would include any strong ace.  I would go as low as A 9.  I would also push with any pairs.  Now, position is still important here.  If you are below 8-10 bb's  I would be pushing from any position but if you have 8-10 or a little more I might wait for a middle position or better type spot to push thereby lowering the chance of someone having a better hand and calling.

Remember the gap concept starts to play a bigger role at this stage and any callers most likely will not be calling with a marginally better hand ... they will have to have a great hand and if there stack size is average or a little better/worse, chances are they won't be calling.  You still have some fold equity at this point.

If you have an average stack entering this stage I would be playing solid abc poker.  No early or middle position limps or small raises.  There's nothing like limping with AQ and 2 positions later you have an all in !  How good does your AQ look now ?  At best I would say you're a coin flip.  At worst you are dominated or crushed.  Now if I had AQ on the button I would put in a raise.

Maybe its just me but at this point I like to be a little more aggressive and raise 4x the bb and not the usual 3.  I always like to put in just that little extra because I think it really puts the players left to act to the test.  Even though they(the blinds) have money invested in the hand chances are they will not call with hands like A 10 or K J because you have put in that 1 extra bet.  Your pricing them out of the hand.

Now the best part.  Your cruising into the middle stage with the chip lead ... or close to it.  Here you have the luxury to pick your spots.  The blinds are not a factor to your play yet and you have 100% fold equity.  An all in by you means your opponent is playing for his tournament life !

I would be very aggressive with any of the premium hands in any position and 5 bet the bb at least.  If I am on the button or cutoff and have hands like AQ, JJ, AJ I would be stealing the blinds.  Any other hands in any other position sees me folding.  There is no limping at this stage.  You can just get into to much trouble limping and more often then not it costs you.

I think the size of your chip stack invariably dictates how you will play in the middle stages of a tournament.  You must be flexible and shift gears when needed.