As in every poker game, there are tells that can be noted during online poker games too. Here's a short list of online poker tells that will help you sharpen your skills and spot the weakness of your opponent during an online game.

Playing against more experienced solid players, amateurs risk the possibility of being ripped off.  One of the most important things to look for is the size of your opponent’s buy-in with regards to the maximum possible amount that's allowed. Skilled players often buy in as close to the maximum table limit as possible in order to maximize their chances.

Following this logic, beginners usually  buy in only for a smal amount that is somewhat closer to the minimum. This is how weaker players protect themselves from suffering a potential loss. Experienced players at the table will surely know that this is a certain sign of weakness.

Finding out how many tables the opponents are playing simultaneously is another sign. A multi-tabling opponent is a solid adversary.
One well guarded secret from the world of online poker tell is as follows: a quick bet on the turn or river usually means a strong hand, also a  quick check could mean a weak hand.

If the opponent checks followed by a raise, the check could well possibly have been a bluff, trying to catch you unaware.

Hope these few tips will help you making better decisions during a poker game.