Nice post.
As for me personally, I don't ask myself any questions as such. I guess it's just years of subconscious practice.
I guess I can outline the process as follows:
1. Calibrate your alarm system by getting a feel for the environment. Your level of alertness should vary under different conditions: moving around a night club is very different from your nephew's birthday party.
2. Be aware of your immediate surroundings. Listen with your ears and smell with your nose. When there is someone really close by, most people can feel the presence without seeing.
3. Scan the environment ahead. Don't look at people, but look past them. By looking past them, I can observe an individual without looking suspicious. Glance, rather than stare. Glance far ahead at several points, and then glance at the ground in front (aware of obstacles). Use of peripheral vision is important.
When you're in an unfamiliar location, try to look like your looking for something (don't exaggerate!). This eases suspicion from passers-by, and makes you look natural.
Tips: move head rather than just eyes. Enjoy the scenary.
When you're in a familiar location, try looking executive, and walk strongly with purpose.
Tips: move eyes rather than head. You're going somewhere, so people had better move out of the way!
My 2 cents.
