Whether you play live or online you are going to run into the same "regulars." In a live game you can recognize them by face and remember how they play. When you play online, you have to rely on something else.  You have take notes in the software about how your opponents play.

As you are playing you should always be observing your opponents. You are hoping to find out their tendencies. When they have a big hand, do they slow-play it or bet it out? Do they fast-play draws? How often do they continuation bet? And so forth.

All of this information is extremely valuable to you, and as you get a feel for individual players, you should update your notes on them.

You'll learn to love notes when you're three hands into a session and your opponent bets into you on the river when the third flush card comes. You check your notes and see "Likes to bluff three-flush rivers out of position."

Leaving yourself detailed notes not only helps you pay attention to your game and your opponent's tendencies, but ensures that if you run into that player again, you will already have a step up on him.

Poker is a game where reads are key. If you have more information on your opponent than she has on you, you will get the better of your battles. So do yourself a favor and take detailed notes on your opposition. Your win rate will thank you.

If you're looking for some more advice on note taking, check out Take Notes: Future You Will Thank You.