Here’s a small tip I try to use as often as possible, though distractions can sometimes get in the way. When you’re heads-up and waiting for the turn or river, focus on your opponent’s eyes and facial expressions rather than the card itself. Many amateur or recreational players reveal a lot of information through their reactions—whether it’s the card they’re fixated on, how quickly they glance back at their hole cards, or other subtle cues.
One other thing: you’d be surprised how much a little alcohol can affect a player. That small sigh or subtle huff when the card doesn’t go their way is a dead giveaway. When I catch those tells, regardless of whether their action is passive or aggressive, I almost always come over the top to apply maximum pressure.