Know thy enemy!

It's actually easier to bluff good players than bad ones. They're more predictable.

A bad player may not even recognize the "scare cards" you're insinuating you have.

Most good poker players will bail at the first sign of trouble -- a potential full, flush or straight on the table -- assuming they don't hold the rest of it. They make their money on the hands they CAN win, not the ones they MIGHT win.

Why shouldn't they? The game of poker, at least online, goes on forever. A good player can fold hundreds of hands that MIGHT have won and still make plenty of moolah on the ones nobody else can touch.

Unfortunately, for them, this also makes them predictable. Bluffable.

If you watch your opponent(s) awhile, you can learn what constitutes a small, medium and large bet for that person.

Based on that, you have a lot better chance of "putting" him or her on a certain set of hole cards.

When there's A-9-4 on the flop, and they throw out a LARGE bet (Large for THEM, not you) you can rest assured they've got a pair of aces.

(Assuming they're not a bluffer like you or me, using the WonderBra approach to make a pair of fours look like a pair of Aces...)

Most people can only handle so many boxes mentally - small versus large, or small, medium and large -- that and the mechanics of chips or online software makes certain size bets convenient, compared to an entire rainbow of amounts.

Which gives you a clue to what's actually in their hand.

You need to know if your opponent will slow-play because, when they merely call despite having superior cards (like 3 of a kind) a call gives you NO USEFUL INFORMATION.

Slowplaying will often reveal the skill level of your opponent; a total beginner never does it, an intermediate does it too often, and a pro will do it selectively.

Determine what hands your opponent will raise pre-flop. Royalty only, pocket pairs, or Ace or King-anything.

Someone who raises pre-flop only with Royalty (A-J, or K-Q,...) who then turns around and bets big when only numbered cards (2-9) hit the flop, chances are they're bluffing.

Most of your successful bluffs, you're gonna have a low pair, they're gonna have a medium pair, they'll see a high pair on the table, and that's it.

You may OCCASIONALLY convince the holder of a straight you hold a flush.

Knowing your enemy will give you a much better idea what he's got, and the chances of bluffing him out of it.