I studied body language heavily early in my career to get by, so I might can help a little.
-Usually lack of eye contact can be considered dislike, avoidance, exclusion, nervousness/lying. Maintaining eye contact usually means the opposite, acceptance, interaction, interest in general (not just in speaking, but possibly love/lust), and confidence. So the first part may be unintentional because you aren't doing the second part.
-Posture also plays a role, sprawling out in a chair shows that you are comfortable, confident, and can sometimes be seen as an act of rebellion or aggression. The opposite of sitting up straight, legs under your chair can show formality, insecurity and guarded from others. Fidgeting can show nervousness/untruthfulness, and slouching can show disinterest/boredom/extreme insecurity.
-Arms are another element, crossed arms shows you are guarding yourself, arms on your legs show you are open to talking, and occasionally showing hand movements to direct your speech is considered interaction (there are a lot of these, usually used in describing movement or size). Hand gestures such as interlocked fingers or thumbs and forefingers pressing together can be seen as a sign of suggested dominance or a "better than you" attitude, leaders in a group tend to use this, it isn't always an underlying insult. A good bit of the gestures depend on the situation, but generally have a similar meaning.
I've found these can be even more influential than facial expression in the long run, and you can practice by watching for these signals on the news and other TV shows. I still have problems integrating these and can often go completely un-noticed in a group, which is surprising for a 275 lb man.
_________________
BAP: 103 aloof / 100 rigid / 103 pragmatic
AQ: 40 EQ: 8 SQ: 114
Aspie: AS-156/200 NT-56/200
RAADS-R: 189 total
Diagnosed 9/2013