Poker is a game of information, the more you have the better decisions you can make. The easiest way to get information is by observing your opponents. Since we're playing online that means noticing their bet size, position, and the hands they play.
While playing recently i realized that i make certain generalizations about my opponents based on what i observe from them.I will go over a few of the basic assumptions;
I don't pay much attention to this in the early rounds. But later when blinds are >200 and I'm looking for an easy way to accumulate chips i note those who are limping a lot and inappropriately. Eventually i will shove over them with air and take the free chips.
I take special note of opponents who limp UTG and those who limp monster hands in general. This info can be very useful since i will gladly limp behind these guys with SCs when in LP.
Playing weak hands
Recently in a $4 180 sng on Stars an opponent showed down K2s winning with a flush after limping and calling utg. In another hand an opponent showed down QTo after limping and calling a raise in MP, then went to showdown with TPWK.I was not involved in either hand but i was able to learn alot of usefull info on both opponents, both of whom won their respective hands and had nice stacks.
K2s Opponent: This opponent has no concept of position. He/She will likely play any broadway, All suited Aces, and probably most Ax hands. Generally this is a really bad player.
QTo Opponent:This opponent will also play any broadway and most aces. But my note on this player will have alot to do with how he played post flop. He overvalues TP and will stack off with TP with a weak kicker, definitely good to know.
Bet sizing can give away a ton of information, this is why most books and sites will tell you to keep your betsize consistant. Many opponents don't seem to realize this and will basically tell you when they have a monster or a weak hand. So i look for hints of hand strenght both pre-flop and Post-flop by noting the size of my opponents bets.
Of course no two opponents are alike so while a min raise utg may be a weak hand for one player it could mean a monster for another. This is why observing opponents when you're not in the hand is so important. Anytime i see a min raise i perk up and start taking notes.
I also take note of sudden changes in bet sizing. Most opponents will regularly open with 3xbb raise but suddenly they change to 4x or +5x. I see this alot in micro stake tournaments, especially in EP. It will usually indicate strong but vulnerable hands like medium pocket pairs 88-TT but most often it is AQ+.
There's a ton of information at the tables, I could go on forever. Its up to us to observe, find patterns and take advantage of our opponents weaknesses to make lots of monies. Remember if you fail to note an opponent who overvaules TP and then proceed to stack off with AK on a T high flop because you raised pf... well thats on you, you're the donkey!