Take your tricks early, and take tricks with only the cards you intend to. taking extra tricks usually result in bags. However, if someone trumped your king of diamonds, you better win another trick.
If you don't have the Ace of Spades, but have the King and/or Queen, try to force the player with the Ace to play it. Usually, you flood spades with low (2's or 3's) to force out higher. If you play a higher spade (5, 6, or 7), others may play lower spades, and you take a bag. The point behind flooding spades is that if you lead a spade, all players lose one spade if they have one.
Grab the Queen and/or King when you can. If the other two players led spades, it is a good time to play the Queen and/or King (if that will win the trick). If you have a lot of spades, however, try to wait until the end, since the Ace will likely be forced out before your King will.
When you have all your tricks, or are missing one with the Ace of Spades in hand, dump every trick if possible. If you have to take a spade trick, take it with your highest spade to cut damage.
You bet blind (bet without looking at cards) when you are far behind and/or another player is close to winning. The best time to go blind is during a game you bet last, since you have an idea how good or bad the other hands are.
For three player, remember that there is one card missing. If that card is low, it usually doesn't affect the game. If it is high, it does. If the trick comes to you, the ace hasn't been played, and you have the King, or Queen (if ace and/or king haven't been played), play your King or Queen, since, possibly, the higher card is missing.
Once in a while, the Ace of Spades is missing. This really messes up the game, since three guys scramble to win their high spades to protect them from the Ace, and the Ace isn't even in.