Body language isn't something to learn in the traditional sense.  It is something that we already know, though we know it subconsciously.  "Learning" body language therefore isn't about acquiring a new knowledge set.  It is about "unlearning" what prevents us from accessing the information consciously.

  For example, examine this picture and notice how your body feels.  Running your mouse over it will change the character's body language.  How does it feel to you after the body language cue is revealed?  Did you notice a change in the quality of what you were feeling?  If not, that's okay.  The information we are looking for is rather subtle, so let's keep trying.

Consider our next example.  Here, the reaction occurs in the other shoulder.  When you move your mouse over the picture, did your feelings shift in a different way than during the first picture?  That is an indication that you already "know" body language cues.

  Consider the picture to be an acquaintance to whom you have just offerred to buy dinner.

  In the first instance, the left side (female or emotional side) reacts, indicating an issue with receiving.  Perhaps dinner sounds good, but they'd rather split the check.  Or maybe your offer feels like an unwanted advance.  Either way, there is an issue with receiving.

  If our offer of dinner is met with the body language in the second picture, then the reaction comes from the male or intellectual side, indicating a possible issue with giving.  This person could be interested in dinner with you, but they are wondering what they will be obligated to give you in return.  Or perhaps they believe that you are really offering them an opportunity to buy you dinner.  Either way, this person is weary of becoming obligated.

  Examine the animations again and notice how your body feels as the subjects react.  Is the difference in quality of what you are feeling becoming a little more obvious?

  Let's take another example.  Here, when you run your mouse over the picture, this potential dinner date is releasing an issue rather than activating one.  Your date is no longer anticipating or wondering if.  The body language is saying "I'd thought you'd never ask."  Or it could be "phewwww, I wasn't sure how I was gonna eat tonight!"  In any case, the body has become more relaxed.

  So, which of these three is the best dinner date?  Well, that actually depends more upon your body language and issues than your acquaintance's.   "It takes two to tango" so to speak, and therefore we naturally (unconsciously) gravitate to others whose issues dovetail with our own.  If we need to be in control of social situations, then dinner with someone who is willing to defer to our desires will flow most easily, as in animation number one.

  On the other hand, if we are looking for someone to "take the reigns" and "make things better" for us, then the character in the second instance will yield the best connection:  this person will (generally speaking) set relationship boundaries and negotiate obligations early.

  Tragically, this dovetailing perpetuates our latent patterns and prevents us from simply being ourselves, in the moment.  If our desire is to have dinner with someone who simply enjoys us for who we are, then that last candidate has already fit the bill.  The dinner request has released an issue, not recreated one.

  Of course, life and body language are not snapshots.  They are vibrant, ever-changing movies.  This short primer is simply meant to illustrate both the subtlety of the knowledge and its relevance.  The little snaphots above are not meant to be actionable examples - don't go accusing anyone of having obligation issues just because their right shoulder moved.

  We always make the best possible choices from the information that is available to us.  Therefore, if you train yourself to move your knowledge of body language from the background (preattentive or subconscious mind) to the foreground (conscious awareness), then you will have conscious access to more information from which to base your choices.