One mistake that I see online players make frequently is the way that they play small pocket pairs, especially from early position.
Small pocket pairs can be dangerous, particularly online, where you have so many players playing such wide variety of hands.
If you are not careful, you will simply end up building a pot for someone else to take away.
Here is an example from a hand that I played in a 9-player Sit n Go last night.
Early on, the blinds were $30-$60.
A player under the gun made a  2x raise of $120.
I was in middle position with A-Q of hearts.
I decided to re-raise to $240 to try and better define the situation and eliminate some of the limpers that always want to play every hand.
A 2x Big Blind raise will not scare off the limpers, especially with the blinds this low.
The under the gun player made the call after everyone else had folded, leaving us a pot of $570.
The Flop came Qs-3h-2h.
I have flopped top pair, top kicker, with a nut flush draw.
My opponent leads out with a standard continuation size bet of $360, fairly reasonable in this situation.
I figure him for either  a mid pocket pair or something like A-K trying to test the waters.
I call, mainly because of my flush draw, but also in case he has flopped a set of 3's or 2's The Turn card is a Td.
He check and I am content to do the same, again, hoping to give him a little sense of false confidence and possibly hit my flush on the River.
Sometimes simply making this check will result in your opponent getting overly frisky on the River.
It is seen as a sign of weakness, and looks like I just called his bet on the flop to see another card.
  There is now $1290 in the pot.
The River card is the Q of clubs giving me a set of Q's.
My opponent bets another $400, into a $1290 pot, I re-raise him all-in.
He makes the call, probably feeling pot committed and turns over pocket 5's, obviously losing and busting out to my set of Q's.
You can say this is a poor example because this guy was a knucklehead, but this type of play happens more than you think.
He simply convinced himself I was playing A-K and he had me beat, I guess.
You are not going to end up with all of your opponents chips in this situation every time, but the point is, he was simply building a pot with a low pair.
This is a dumb idea in online No Limit Hold em.
Let me say this, I like to limp with low pocket pairs, especially in early position.
You only chance with these types of hands is to hit your set.
If you do not hit your set, try and see a free card on the Turn.
Otherwise, lay it down.
Think about it.
The only hands that are going to call your pre-flop raises are hands that can beat you like a higher pocket pair or A-K, A-Q, A-J, K-Q etc.
If an over cards comes on the board, you are already beaten 9 times out of 10.
Someone is playing an over card and you have done them the favor of building a pot.
Let them do their own pot building, don't do it for them.
In the above example, the player with the pocket 5's should have checked after the flop, or at least not wasted anymore chips after his continuation bet was called.
Even at that point, however, he would have spent $500 in chips building a pot that he was going to lose to anyone with a Q in their hand anyway.
This is not smart poker and it is an area where many online players need work.
Early in a tournament, limp with low pocket pairs and you will find that you save yourself alot of chips.
You will also get paid off more when your set does hit.