The one I'm going to practice is not being biased:

If you already like or dislike the person it's going to affect your judgment. And if people compliment you, are similar to you, are attractive... these can all sway you, unconsciously. I know, you don't fall for those tricks. Well, the biggest bias of all is thinking you're unbiased.

How studying body language changes the way we socialize.

How to get better at reading body language

First, pay attention. Sounds obvious, but you're probably not doing it consistently throughout the conversation.

Dynamics change, especially when you're dealing with someone who is actively trying to deceive you. Unless they're very good, inconsistencies will arise ("leakage") and you can get insight into how they really feel.

You'll improve dramatically by addressing the four weaknesses pointed out in The Silent Language of Leaders:

• Consider context: Should someone in this situation be acting like this?

• Look for clusters of actions, not isolated ones: All three of those behaviors are associated with…?

• Get a baseline: How do they normally act?

• Be aware of your biases: Are you tempted to cut them slack and they haven't started speaking yet?

Your abilities will make a quantum leap if you realize that body language is part of a bigger context and a bigger cluster and you start monitoring the other facets of behavioral interaction: voice, appearance, clothing, etc.

These can help you evaluate the whole package:

• What does clothing tell you? How about shoes?

• What does someone's voice tell you?

• What does a face tell you? How about a quick glance?

• What are 10 instances when you should trust your gut?

Read more: 

http://theweek.com/article/index/260715/4-secrets-to-reading-body-language-like-an-expert