A tell is something that a player says or does that can give an observant
opponent insight as to what cards they are holding and what they are
thinking. The best poker players in the world don't rely only on their
skill and the luck of the draw. They learn to read subtle clues from the
other players to help them see strength or weakness in what the other
players are doing.
Common tells are licking of the lips, the way they hold their cards or shift
their cards, shiftiness in the way they look at other players, or the way
they idly fumble with their chips. You may notice two kinds of tells - both
represent the level or stress, anxiety or confidence about the cards in the
player's hand. The first are more obvious movements that come out as
shifting cards, leaning forwards or backwards in their chair, and changing
their betting patterns. These are the tells that professional players work
very hard to control and hide. The other type of tell are individual to the
player and much more difficult to hide as they are subconscious
idiosyncracies - these may include pulling an ear, holding the chin, rubbing
their hands, and are important to watch for since they are just as
revealing.
The important thing about tells is that it's not enough simply to notice the
behavior, you have to link the tells you've seen with the pattern of
behavior; to note when they've bluffed and when they've come out with a very
strong hand. The best way of keeping track of this is to watch each player
when they first pick up their cards, and when they are about to make bets -
look for any outward signs and then connect these with the results of that
hand. It requires that you keep a lot more in mind through each hand, but
if you can, you will have a large advantage over your opponents.