There are generally two types of loose players that you are bound to encounter at the table and they are the loose/weak player and the loose/strong player.
The loose/weak player is an opponent that will give you opportunities to double your stack because they like to play a lot of hands pre-flop. They also lack the experience and skill to play good poker post-flop. This means that you have a double-advantage of profiting from these players before the flop and after the flop.
A good example is when you are holding AA’s. When you are playing against a loose/weak player, you should always raise or re-raise your hand pre-flop, because the loose/weak player will always call that raise. Why not try to get as much money into the pot as possible? Even if you are not holding a premium hand it is still possible to profit off of a loose/weak player after the flop.
Suppose you are holding 7-8 suited and your loose/weak opponent makes the standard 3x pre-flop raise. Depending on your position, you have a couple of options. If you are in early or middle position, you might want to fold your hand and wait for a better spot against your opponent, because there is always a chance that someone behind you may re-raise and suited connectors just aren’t that strong of a hand. But if your stack is large enough, you could decide to call your opponent and try to out play them after the flop. However, without a premium hand there is absolutely no reason for you to re-raise to build a bigger pot before the flop.
Let’s play out the scenario as if we have called (the loose/weak player has made the standard 3x bet) with our 7-8 suited connectors and the flop falls 7d, 9s and Qs. This isn’t bad, it gives you bottom pair and a flush draw, but it isn’t that great either. By keeping the pot small pre-flop, you give yourself options on how to proceed with the hand. With a pair or a flush draw it seems like an easy choice to call or raise a c-bet, because if they check you, you can bet the hand on your own or you can even fold if you become suspicious or suspect that you are behind. By exercising pot control with your speculative hands, you put yourself in a situation where you may be able to win a good sized pot with just a small pre-flop investment or you give yourself the option to avoid an expensive loss.
In contrast, the loose/strong player is very good at post-flop play. If you’ve identified a loose/strong player at your table, you need to be more selective about the range of hands that you play. Hands like small pairs or big suited connectors are great because if you hit you can play aggressively, and if you flop air you can fold easily. Because this type of player thrives ‘post-flop’, taking advantage ‘pre-flop’ will become much more profitable. One of your most profitable plays will be when you look for spots where you are the last pre-flop aggressor. Then you’re the one who is putting in the four-bet and you're the one applying all the pressure.
The idea of taking this aggressive action against the loose/strong player is that you can get them to fold with marginal hands before the flop. Sometimes they may also call, with a real hand of their own, but often times, loose players are not going to be very strong when they raise. Be sure you take advantage of them before the flop!