Heh.
So, really.
The main thing about poker is not to be predictable. If the other players know you only bet big if you have a good hand, you'll never win any money. On the other hand, if you bluff all the time, they'll catch on and clean you out.
Generally, with betting, the idea is that a small bet will keep other players in the game, and a big bet will (presumably) scare them into folding. If you've got a good hand, you want to keep people in the game and suck as much money out of them as you can.
If you're bluffing, you want to get their money, but at some point you have to get them to fold -- figuring it's not worth the risk to find out whether you've actually got a decent hand.
[ETA: They'll also weigh the risk against how much they've already bet on this hand, and how much they have left. A ten-dollar raise may be a big first bet in a small-stakes game, but not so big if you're already in for fifty. Then again, if you're down to your last ten bucks, you might think more carefully.]
So, when bluffing, a person may lay low for a while and then spring a big raise. Or, they may start out big and hope to steal the pot.
Somebody with a great hand isn't going to try to scare everybody off until there's some money in the pot; why waste a full house just for the kitty?
But, again, the trick is not to play it the same every time -- as soon as the other players can read you, you're sunk.
Hope that helps a little more, Bravo.