Your first step is to remain objective. No preconceived notions about them, just the facts that you are seeing right in front of you. Use logic, though it should be known logic won't tell you everything. This also requires non-linear thinking skills. Pure logical deduction and Sherlock-ing won't get you all the way there. It gets you close, but not quite there. Observe comfortably and don't over-analyze.
Body Language
How are they dressed? For instance, did they put a lot of effort into appearance or just roll out of bed with their hair still a mess. This may tell you some about income, too, if you're curious about that. Are they wearing any symbols, religious or otherwise? That tells you a lot, too. Amount of clothing shows comfort level. Examples being, if a woman runner isn't ashamed of her mid-section and legs and is running in the middle of the city. Say a second woman runner is all covered up from leggings to breathable shirt behind the first woman. What you are comfortable wearing and showing off reveals quite a lot about your comfort zone and confidence.
Posture is another main point. If they hold their head high and walk with secure footing that's confidence, or a facade of it if they are faking it. A less dominant pose may mean they are less confident, or just less dominant in personality. Ego is revealed here, too. If they walk like they are the Queen or an action star they probably have a large ego.
Physical movement is part of this, too. Leaning is usually reserved for those we like or are close to. Your person may lean toward someone, or look toward them when a joke is told, or both. You close yourself off when you cross arms and legs, like you are defending yourself. If you do cross your legs naturally, you point your toe toward the one you are most at ease with. Hiding hands, in laps, pockets, and behind backs shows they may be hiding something. Or they aren't comforable. It depends on the person, frankly. Biting nails and lips is an anxiety-related thing (not that they have a disorder, though it is possible, but that they are nervous in some form). It eases tension, even if it isn't healthy to do physically.
Facial expressions are another thing. Clenching is a sign of tension. Any facial expression we use often can be somewhat etched on faces, to varying degrees. Also, the changes in facial expressions and reaction should be noted. For one thing, do they mirror your emotions? If they do they are extremely aware of them. Can you not read their emotions well? They may have a resting face (some have a resting face that is a smile, others a flat face betraying no emotion). It gets harder to read resting faces, but the eyes are the window to the soul. If their eyes betray nothing you may have to let them warm up to you.
Intuition
Intuition, or your guts feelings, are hard to explain. They aren't logic. It is the act of directly and immediately perceiving a fact without logical evidence. Some people don't function well intuitively, while others do. Most that do this well are introverted in personality.
That being said, when reading people you sometimes just know that something is off about them, or that something is great about them. If it feels wrong, don't ignore it. If it feels right, don't ignore it. I'll make this short and sweet. Don't ignore a gut feeling about someone. It may save their or your life, in some cases. In other cases, you may just find that they are destined to be your close friend or soul mate. Intuition can sometimes tell us if an individual can or can't be trusted.
It would, however, be wise to think before you act on anything intuitive. We can be wrong some of the time. We are not perfect. All the same, don't ignore it.
That being said, when reading people you sometimes just know that something is off about them, or that something is great about them. If it feels wrong, don't ignore it. If it feels right, don't ignore it. I'll make this short and sweet. Don't ignore a gut feeling about someone. It may save their or your life, in some cases. In other cases, you may just find that they are destined to be your close friend or soul mate. Intuition can sometimes tell us if an individual can or can't be trusted.
It would, however, be wise to think before you act on anything intuitive. We can be wrong some of the time. We are not perfect. All the same, don't ignore it.
Emotional Energy
If you sense emotional energy already you are probably an introvert. To explain it simply, people give off energy based on their emotions. Being able to sense emotions helps when it comes to reading people as a whole. This has to do with empathy, too.
I have said before that the eyes are the window to the soul, and I am saying it again here. Look in people's eyes, see how they respond to everything. It will tell you most of what you need to know, if you are good at sensing people's energy. It takes practice to do. It truly reveals personality, but only if they are not masking their emotions. It is possible to mask emotions.
Physical touch is at play here, too. There is physical energy given off in every touch. Is it comfortable? Warm? Does it make you want to run into the next room and lock the door? That's physical energy. Limp handshakes, firm handshakes, shaky hands, all signs of personality and who someone is.
Vocal tone is a good indicator of personality, too. How loud they are speaking, softness or hardness of voice, and speech patterns are important. It can also be telling on what they care about. What they talk about is equally important.
Sources:
https://www.psychologytoday.com/us/blog/emotional-freedom/201402/three-techniques-read-people
https://synctuition.com/blog/science-supporting-intuitive-thinking/
Pictures:
Thrive Global
Kind PNG
Soft Skills Training
Psychology Today