First, pay attention. Sounds obvious but you're probably not doing it consistently throughout a conversation. A simple bit of motivation can make a real difference. When I spoke to Maria Konnikova , author of The Confidence Game , she said:

When your motivation is high, you actually become much more accurate at judging other people accurately. Most of the time, our motivation isn't very high because that takes more of our resources, but when we're motivated, we suddenly become much better judges of character. We become much better able to read cues. Then you start being able to discern certain things.