a lot of players lose a lot of money defending their blinds. A leak in their game.
that said, if you don't defend your blinds sometimes, that is a leak in your game too and you will be attacked ruthlessly. (by me...ha ha ha )
I assume you are new, since you are posting in this section so I'll start with the baby steps strategy.
Obviously defend your blinds with premium
hands. duh! self explanatory
Additionally try these loose guidelines on for size:
defend 50% of the time vs. a button raise if you have a playable hand.
defend 33% of the time vs. a cut-off raise if you have a playable hand.
defend 25% of the time vs. the hi-jack if you have a playable hand
don't worry too much about defending your blinds against earlier openers, as they are more likely to have a real hand.
How to defend? you can either flat call the raise, then lead out on the flop. (I do this about half the time)
Or you can re-raise pre-flop. This is much more effective when you have a tight image at your table.
Obviously stack sizes and hand strengths matter a lot for which type of "defense" you use.
adjust those guidelines based on stack size, tourney stage, villain's raising range, player read etc. If the tightest guy ever raises you all in from the button and you have A8 suited you don't have to call THAT guy...