What are poker tells? Tells are often described as a twitch of the nose, a crease on the forehead or a physical clue of some kind that alerts you to what your opponent is holding. You'll often hear poker greats talking about reading their opponent's hand based solely on a tell that they picked up on. That's great and all when you're playing in a real poker room, but when you're playing poker online, it becomes a whole different story trying to spot online tells.
1. Watch the Eyes
This is why many pros wear sunglasses or visors/caps when playing, they know that the eyes rarely lie. For example, many players can't help but stare at big hole cards, so their length of time peeking is longer. Conversely, if a player is looking to steal the pot, he may look to his left to see if the remaining players, who haven't yet acted, have quickly glanced at their cards and are likely to fold. Another example, a player may try to ask you questions about your hand, knowing that people rarely can "look someone straight in the eyes" while being dishonest.
2. Trembling Hands
Also, a byproduct of anxiety, beware of a player whose hands are shaking, this nervousness can represent a big hand.
3. Glance at Chips
Again, relating to the eyes. It is common for players to quickly glance at their chips if they connect with the board after a Flop. This may be a subconscious reaction, but the tell is the player is already planning his attack!
4. Body Posture/Attitude
Some players show obvious changes in their posture based on their attitude/hand strength. For instance, you may notice their shoulders drop/slump when they are not confident (weak hand). Conversely, you may notice the player is very attentive and sitting in an erect position when he has strength. You may also notice that a player who bluffs a lot, leans forward in a confrontational way... remember Strong is Weak!
5. Weak is Strong/Strong is Weak
In its most simplistic form, this usually applies to novice players but frequently applies to pros as well. Basically, players like to be actors, and when they have a monster hand they tend to look disinterested. For example: "Oh, is it my turn to act" or "Oh I guess I will play these cards". Alternatively, a player increasing the level of his voice while raising the pot, and trying to look intimidating.. may be running a bluff.