A tell is a change in a player's behavior or action that indicates their possible perception of the hand.
Tells are a part of poker and this social element of the game is what makes it so interesting and popular.
Do you ever play a hand and get a feeling that your opponent is weak, but can't quite work out why? This is likely due to the speed the hand is progressing at. The tells discussed below aren't revolutionary, but be sure to keep them in mind as they might give you the confidence to lay down a huge hand or make a bet that you otherwise wouldn't.
A lot of information can be gleaned from how fast or slow a player plays their hand. Although not obvious, even professional players exhibit timing tells. Timing tells are often instinctive and it's rare that a player understands them or has made a conscious effort to guard against them.
Long Wait & Check
Typically when a player waits a long time (15 seconds or more) and checks it shows that they are weak.
The player is either considering to make a play with a weak holding and has decided against it or is distracted. It is not uncommon for online poker to be played at work or when the user is just mindlessly browsing the internet. These players play recreationally and it is extremely unlikely they would get to the flop with a strong holding and play it strongly.
It is also possible that a slightly more experienced player will take a long time with a strong hand when deliberating bet sizing.
If you're playing a hand where an opponent is checking or calling very fast on multiple streets it's likely they're anxious to get to showdown and finish the hand.
It's not advisable to bet into this kind of player with the hope of a fold as they likely assign some value to their hand. You can certainly bet for value and might find that you earn more when holding hands like 2nd pair than you would have previously.
Waiting for the Big Blind
When sitting down online a pop-up will usually appear asking if you want to 'Post the Big Blind' or wait until it comes to you.
Posting the big blind out of position means that the player will likely pay the big blind twice within a a few hands. If a player does this every time they sit down they will lose a significant number of big blinds over time.
A player who posts the big blind out of position is typically an inexperienced player who does not play professionally.
Generalisations can be dangerous, but in this instance they're probably justified. Professional poker players do not come to the poker table to chat and if they're doing their job properly they shouldn't be distracted no matter how interesting the conversation is.
Have a look at the the general content of the conversation and you can probably make an informed decision.
Number of Tables
The more tables a player is playing the more competent they generally are. A recreational player will typically play under 4 tables. They find a few tables more than enough as they're involved in far more hands than the average player.
Professional players can be found playing 8 or more tables, but don't think the amount of tables being played automatically makes a player great. As poker has evolved a group of players has attempted to make a living by grinding rakeback & VIP deals whilst playing a high number of tables. These players are typically passive and extremely tight. Since they are playing more tables, it's more difficult for them to completely concentrate on the action at a certain table and make an informed decision, so you can definitely exploit this when you think they have a marginal hand.