I read people like a book. In my minds eye, I peel back the pages in order to get an insight into the story of their lives. My accuracy is about 80% and nowadays my ability to read people merely relies upon me glancing at them; akin to Gladwell’s theory of ‘Thin-Slicing’.
The key to reading, is not to draw out inferences based on singular facts like the style of hair or props such as bags or umbrellas, but instead to read clusters of patterns in their entirety. In other words, you must apply some Gestalt Theory; where you consider that the whole to be greater than the sum of the parts.
In particular, I look for congruent patterns as any incongruence is usually significant; for instance smiles that engage the zygotic major muscle, but fails to engage the ocular muscles usually demonstrates that the smile lacks sincerity.
Non-Verbal Cues/Body Language makes up the majority of communicative information. Therefore, failing to learn the basics of body language, especially for the serious martial artist who must establish risk based on how an aggressor moves, can be a dangerous thing indeed.
The martial artist should not only aim to understand aggressive traits, but he should also learn the language of the streets, the etiquette that prescribes how people engage.
Violence exists and it is not vacuum sealed. The posturing, movements, telegraphs all aimed to deceive and distract a victim are cues that can be read.
An aggressor gives away his intentions through a plethora of subtle dynamic tells. So, while you hit a bag, punch pads and spar, consider whether this avenue is also worth examining.