Physical reads play a small role in my overall strategy. At most, I'd say they amount to 5% of my win rate. I spend a lot less time focusing on tells in comparison to most live pros; however, there are a few tells that I find extremely valuable because of their consistency. Some of them have nothing to do with determining what my opponent has. They simply tell me what my opponent is going to do. Many times, that's more valuable than knowing my opponent's hole cards. Allow me to explain.
If you gently disrupt the flow of the game and glance to your left, you'll find that many amateurs hold their cards differently when they're going to fold -- especially pre-flop. Some of them actually fold prematurely. Some of them motion as if they are going to fold. Some of them just grasp their cards differently. Regardless, this is privileged information. It allows you to open wider, c-bet at a higher frequency, and steal extra multi-way pots. Never forget to glance to your left.
You raise pre-flop. The big blind calls. The flop is dealt. Your opponent checks. You've done this a million times. But have you noticed anything? I'm very sensitive to timing. It's business as usual if someone checks immediately. But if that person pauses for a split second too long, he usually has something big and he's trying to resist the urge to bet out. I've also noticed that if someone blatantly takes a longer period of time to check (usually on the river), he's trying to induce you to check behind to get to showdown cheaply.
Most pros never talk during a hand. They know better. There's nothing to gain from trying to talk to another pro. But what about talking to amateurs? I think there's a lot to be gained if you can find a way to maintain a seemingly meaningless conversation throughout the hand, while masterfully gauging someone's baseline, before pouncing on weakness. The trick is to extend the pre-flop conversation to the river. Many times, a genuine laugh will morph into something like this when you start cutting out chips...
Learn to gauge comfort levels. Every part of your opponent's conversation and body language will remain the same until his stack is at risk. At that point, you'll often see a night and day difference in your opponent's demeanor. This only works if you can manage to keep things light throughout the hand. The worst thing you can do is try to start a conversation AFTER your opponent makes a big bet. His guard is up. There's nothing to be gained.
Take some time to educate yourself. Here are a few books that I would recommend. They've all played a role in my development as a poker player. In no particular order, I would suggest reading...
Read 'Em and Reap: A Career FBI Agent's Guide to Decoding Poker Tells by Joe Navarro, Marvin Karlins, and Phil Hellmuth Jr.
What Every BODY is Saying: An Ex-FBI Agent's Guide to Speed-Reading People by Joe Navarro and Marvin Karlins.
200 Poker Tells by Joe Navarro.
Caro's Book of Poker Tells: The Psychology and Body Language of Poker by Mike Caro.
Reading Poker Tells by Zachary Elwood.
Verbal Poker Tells by Zachary Elwood.