You stare a man down and he glances up at you and smiles (this involuntary gesture is invariably an indiction of a bluff) (Unless they're a hardened pro).

They relax back in their chair and spread their arms - commonly a sign that they are bluffing. It is a over-compensation.

The "overtalk" - an increase in the amount of talking, particularly sentences like "i'll give it a go" or "why not" - often an indication they are sat on a big hand. (it is an air of false reluctance). Simirlarly talking can indicate a level of relaxation/comfort, which again is indicative often of a decent hand.

Lack of talk and fixed focus of the eyes can often indicate a bluff. This is one of the tells that good players will eliminate by doing it consistantly regardless of their hand strength, however it is still very often seen.

Glancing at chips immediately after the flop - often an indication they have hit something.

The look away when hit the flop - Very similar to the one above in appearance. It is an involuntary gesture feigning nonchalance. If they glance away when they see the flop come they have often hit it.

Speed of call - A quick call is often a sign of a lack of commitment to a pot. It is mainly feigning strength with a view to hopefully slowly villain down to achieve more streets towards a showdown. It is largely involuntary for any average player.

Spotting the rookies (their tells):-

Relentlessly moaning about bad beats.
Over-defensive when trash-talked to.
The necessity to say 'WOW' or 'Unbelieveable' or 'What are the odds?' etc when they see an uncommon hand or scenario.
Moans about someone else playing rags