How to study opponents?

Always use the software to your advantage. Specially the notes taking part. Write what you see and eventually you will get good at recognizing their weaknesses.

The other tip I have is that if you are going to raise, then you BETTER have a continuation raise right after. Keep them on their heels no matter what cards flopped.

One of the key skills most good poker players have is the ability to read their opponents at the table. That is why you hear so much about “poker tells.” A “tell” is any physical reaction, kind of behavior, or habit that gives (or tells) the other players information about your hand.

Everyone has their own unique tics and tells, and it’s great to watch individuals and pick up on their unique tells. Luckily, there are also a few involuntary and common tells that you can watch for even the first time you sit down with someone. As a general rule, remember that when a player acts strong, he’s probably weak, and when a player acts weak, he's probably got a really strong hand.

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If I put links in this signature again I will get banned.

I agree Joe, however many of today's player are sagacious to the continuation bet, it becomes almost expected, the astute opponent might even take the opportunity to apply a mind shattering raise or re-raise even in bluff form which often cause a "stop it in it's track" or even a takeover, today to be effective takes an expensive double flop/turn continuation bet against those "in the know"

Today against two knowledgeable players that are aware of each other the opposite play can be made "a check", the opponent feels that either you did not hit your flop or ... that you did, or are that strong and are "trapping" take your pick. With the vast amount of poker information out there - today's complex game has become more complex and if you have not picked out the donks from the astute in your game, then the right play could turn out to be the wrong play.

I think that in time you will get the feel of other players, when they are bluffing and such.