Play according to your position
When you have a premium hand, you should usually raise regardless of your position at the table. With AA and KK, you should re-raise. Raising from an early position tends to narrow the field and makes it more likely that your premium starting cards will win. Raising from a late position tends to build the pot since players who already called are less likely to fold. Your premium cards are less likely to hold up against many players, but you will win more money when they do. In either case, you benefit from raising.
Play drawing cards when playing loose amatures
With many players in the hand, you can play weaker starting cards. Drawing hands face long odds on winning, but if enough players contribute to the pot, the potential winnings make it worthwhile to enter with a drawing hand. For example, if you are in the last position and you have a connected straight-flush-draw like 5,4 6, and all the other players have called, but not raised the blind, entering is worthwhile. If the flop comes up 44 74 8, you have a well-disguised straight and could win big if the people holding high cards bet heavily. But the odds of hitting a flop that favorable are low. Therefore, if there are bets from the early-position players and folds from the mid-position player (which leaves only 3 or 4 players), you should fold, as well. The people who called in an early-position have good cards and you will not win enough money in this situation to justify playing for a long-shot draw.
Don't try to get away with pure bluffs
Against tighter players, and players who are serious or even semi professional, the bluff becomes a meaningful tool. However a pure bluff will not work often enough to be profitable. Experienced players will take advantage of a "drawing hand" to "semi bluff", so that even if you are called, the next card can still give you the high hand.