Messages
You can learn empathy: knowing where people are emotionally, right now.
Pay attention the “messages” they are sending out – usually not to you, often to no one in particular. Are they enthusiastic? relaxed? happy? in a hurry? argumentative? tired, discouraged, beaten down or depressed? Watch their face, how they move, and how they choose to present themselves to others. If feasible, note the difference between those going to office or other work, and those returning after the shift is over.
This exercise works best with strangers, when you can observe them without interacting - for example, on a busy sidewalk, or seen from a cafe window. With friends or colleagues there’s often so much going on that it’s better to focus on that and not split your attention for an exercise. Later, observing, listening, and paying more attention to others' emotions will become habitual.
It helps a lot if you can see their faces. But if you can't, notice how they present themselves to the world. For example, what is the most memorable feature of their appearance, or what they are wearing?
More importantly, what are they doing? Are they alone or with others? On a phone? If with others, is one person doing almost all of the talking?
If two or more people are walking the same direction near each other on a somewhat crowded sidewalk, how soon can you tell if they are together, or just happen to be near each other? An advantage of this practice is that you can often keep looking and confirm whether your early judgment was correct.
I explained these practices to someone who said, "Then you can imagine what they are going home and doing, etc." NO! You want to be as objective as possible, to pick up what other observers will likely pick up. Here and now. If you imagine stories, they will be different from the stories other observers would imagine. (Later, Messages could become a group exercise, so you can compare what you observed with what others saw in the same situation.)
Caution, staring is impolite and can even lead to violence. People don’t like being spied on, or being put onto a public stage when they are not ready for that. Grab a quick impression; no need to keep looking. Or maybe practice with videos or movies. I have found it easier to follow the plots and subplots of movies since I have been doing this observing/listening exercise (usually with people not films).
What is the point of seemingly trivial observations of strangers? The benefit is training YOU to habitually be more aware of what's going on with other people, their activities and emotions, what matters to them, right now.
Note: After finishing this writeup I found someone who has done more with a similar practice. See "Fourteen ways to develop Sherlock Holmes-esque perceptiveness that will make you more effective in all areas of life," by Alex Mathers. I will be learning from it.