First of you need to determine when, or if, you are short stacked. There's two popular ways:
- M Factor
- 6x
The M Factor approach, as explained by Dan Harrington in Harrington On Hold'em is to calculate your "M": divide your stack by the Big Blind + Small Blind + all the antes. If you M is low, 4 or less, then you are short stacked.
The 6x approach is to multiple the Big Blind by 6. If your stack is smaller than the BB times 6 then you are short stacked.
When you are short stacked your options are limited. Limping and chasing hands are not viable options. Generally your best approach is to move all in. With 6 times the big blind an all in move can get other players to lay down a lot of hands that they would not if the all in bet was only 2 or 3 times the big blind.
fold equity allows you to move in with weaker opening hands, because you're less likely to be called. Any Ace, small pairs, even suited connectors are suitable move-in hands. Position is still important, so for an all-in move from early position you must have stronger cards than an all-in move from late position due to the fact that you are facing many possible better hands behind you when you make this move from early position. And, while you don't mind getting called, your equity goes down considerably with each extra caller.
You also have to be very aware of when the big blind is coming around to you. If you're at just under 6 times the big blind, you can't afford to wait more than a single orbit, certainly not more than two orbits.
The clock is ticking, and every other player would much prefer to see you limp and fold than move all-in. Frustrate them by attacking. If a player limps, or the small blind limps against your big blind, attacking with an all-in can often win the hand right then and there.
Lastly remember that any two live cards against any other two live cards is usually a close "race". Download a copy of PokerStove and run some simulations. You've going to see some numbers that might surprise you. Even a hand like 67-offsuit has nearly 40% pot equity against a hand like Ace-King.