One thing to always keep in mind is that communication and assessment is almost always a two way street. Many (most?) of us have little understanding of how we might be "understood" or perceived by others.

Years ago I was in a job where I occaisionaly but infrequently had to interview job candidates. Since my training and background was mostly in science and technical areas, my employer sent me to a class on interviewing. One of the things we did was to conduct mock interviews which were video taped. It was really fascinating and revealing to see my own mannerisms, body language, and facial expressions. We then talked about how these might be perceived and misinterpreted by others.

An example of what I've learned about myself over the years is that when I'm deep in thought, my face sometimes appears as if I'm angry or upset (when I'm not, I'm just thinking). In some situations that might be frightening to someone, and they react accordingly.

People will react according to what they perceive in us. Always keep in mind that what you see (negative or positive) in another person might be to some extent a reflection of how they are reading us. You should try to know yourself before trying to know others.