A tell in poker is a mannerism that betrays a player's hand. A tell is not just physical, it could be an irregularity in a player's betting pattern that gives away strength or weakness in their hand. Most players are unaware of their tells therefore are likely to keep producing the same tell in the same situations. Although you can't see your opponents online, with practice, you'll be surprised by how much information you can pick up from a player's reaction time and their betting amounts. Here are a few things to look out for, live and online but remember none of these tips are infallible.

Online

A quick call with 2 flush or straight cards on the flop generally means a draw. Someone with middle pair, or top pair with a weak kicker will often take more time to consider whether a call or a raise is the best option.

A quick raise is generally weaker than a raise after a delay. The delay usually comes from a player considering whether or not to slow-play a good hand.

If a player checks instantly, then they probably had the check/fold button clicked before the action was on them which indicates that they have no interest in going further with their hand. Beware though because a player may also check very quickly if they flop a very big hand hoping to trap someone. It's up to you to decide which is the case.

Before or on the flop, if a player looks at his chips then he is likely to have a strong hand.

If you notice a player's hands are shaking, don't automatically assume this is a bluff. This could be caused by the adrenalin from holding a really big hand.

If someone starts looking around the room as if disinterested in the flop, tread carefully. Many players pull this act when they have flopped a big hand.