You need to make this decision based on your stack size and the blinds. If you start a tourny with 1500 and get to 900 with the blinds at 10/20 20/40 30/60 you can still play some poker. There is really no reason to just shove all in, you will not have any value. when the blinds are a bit bigger you should shove and not wait for a premium hand. I usuallly wait for a spot in late position with a semi strong hand , but do like to push in early position with only premium hands, as you have the chance to be called by more players.