The players who have tells are so abysmal in their play that it's a moot point.
I don't agree. There are solid players who are prone to giving away information with their body language.
The biggest thing if you're looking for tells (that you're actually going to use as part of the decision making process) is to establish a baseline. Watch the way they say or don't say the word 'check', or the way they push chips forward when the bet/call. Watch them watch the flop - what patterns can you establish?
Sometimes you can induce a tell. One time in a tournament an opponent made a sizable river bet into me on a very straighty board while I held a modest 2-pair hand. He sat stoic as I pondered a call... then I started talking to myself out loud. I carved out a call out of my stack and said '
what's this going to leave me with', as I observed his posture. When I said this, he swallowed nervously. That was the information I needed to make what would turn out to be the correct call.
Another time against a player I have a ton of history with, it was late in a tournament where as the big stack I was raising often. I opened with A8o... and the player in question jammed over the top from the BB for about 1/5 of my stack. He immediately began jabbering like he often does when he's pretending to be comfortable.
After about 30 seconds of pondering, I asked for a count and said out loud '
I have the same hand I folded last time'... referring to a hand a few minutes prior where I folded a modest ace to an all in bet. After I said that, he stiffened up, folded his hands in front of him and stared forward at the center of the table and didn't make another sound.
He was clearly trying not to draw attention to himself. I assessed that his banter was a 'strong means weak' tell and ultimately made the call. He turned over A5.