When to sacrifice pieces?

When should you sacrifise chess pieces? Giving tips would be helpful and showing some examples of when a sacrifice was done. Thanks.

Sacrifice peices when there's nothing better to do.

Seriously, that's how I decide whether or not to sac in my games.

Sacrifice if it will win you material (I know it sounds weird, but a sac can lead to material gain), gives you a mating net that is unstopable, prevents your checkmate (If you would rather play a game to its end than resign), prevents the loss of a piece worth more (sacrifice a knight to save a queen, etc.), or creates a position that is better for you than it is for your opponent.

Sacrifice whenever it's better than not sacrificing. 

Don't be shy -- if one or more sacrifices leads to a crushing, irrefutable attack that'll checkmate your opponent (or, get back your material and leave you with an advantage), then you ought not hesitate.

sftac