Mike Caro is a man worth listening to.
Nicknamed “The Mad Genius” he’s written a butt-load of stuff about poker, including statistical contributions to the biggest poker texts in the world.

This video will be very useful to beginners and will give you something else to look for to get extra information out of your opponents.
Watch out for what he calls “the pokerclack”, it’s a dead giveaway.

Monkey Thinking:

Tells are the reason you shouldn’t listen to music/watch videos/read books/masturbate whilst you’re playing. How can you spot anything like this if you’re not paying attention?

The best time watch players is when you’re not involved in a hand. Every time another player’s cards are exposed, work backwards through the hand in your mind and identify their individual behaviours.
When you’re in a hand with them, are they doing the same thing? Odds are, they have a similar holding.