I came across this on holdem.com and thought it was a great read

ddAggressive bets and hand play in poker is good, but these must conform with a particular poker game context. And poker aggression must also be seen against the backdrop of other poker skills like reading, assessing, and making the right decision.
When we have a strong hand and we bet aggressively we force other players to pay off. An aggressive caller is so in hopes that another player would pay the caller off. Hence, the advantage in poker aggression especially for the player who plays hands rigidly but is a little soft on the bets may still win lots in limit than in no-limit. Hold'em tips recommends to be sly with hands and aggressive with the bets when called for.
Each type of poker requires different aggression levels. Short poker games may require looser hand plays if other players seem too tight. But when they're all casual with the play, we must double our caution in playing, because their looseness may mean they have strong hands. So the principle of opposites applies here: With a lose game, be rigid; with a tight game, loosen a bit to mislead or get them off guard and then we steal the pot.
Playing no-limit sometimes also means adjusting to an opponent's play. If the opponent shows a weak play, Hold'em tips suggest we go easy on the bets. Don't scare them off with aggressive bets�this is our grand time to milk players of their bankrolls and make a real killing�and just loosely and coolly play along with minimum bets, as if we're on their level. However, it's entirely another thing when we're in a crowd of good players. We play hard and bet cautiously.
Poker aggression should also go with reading skills. We should have an idea of what the opponent has. Of course, this is not acquired overnight. But for starters, where are Hold'em tips for reading cards: pay attention when a player bets or calls a bet. Then ask ourselves why the player did that. For sure, it has to do with: What the player has, what the player thinks we have, and what the player thinks that we think the player has.
Poker aggression is a powerful tool for winning, but it can also be a power to wreck our play when put to wrong use. Being aggressive in itself is no guarantee for winning, but put in the right perspective�with skills in reading and assessing�aggressive plays and bets can help us win.