OODA is the acronym of power in powerless situations. Used by military and police forces in the USA and abroad, it describes the process of perception which aides situational awareness. But it can be a effective tool for anyone in any unfamiliar or potentially dangerous situation.
Observe- Keep a 21 foot bubble of awareness around you in which you know where everyone and everything is. Use not only vision, but sound, scent, and any intuition you are blessed with in being focused on all events in the immediate area.
Orient- When something (or someone) catches your attention. Focus in on it. What is happening that caught your eye and why did it happen? How could it effect you?
Decide- Escape, confront, avoid, ignore, attack? Once you've identified a potential situation, decide what to do. Don't dwell on options for too long; go with your gut.
Act- Move in a proactive fashion, without hesitation. Continue until you've completed the action you decided on. It is no good to contemplate your decision until you have followed through on it.
Once you have acted return to the beginning of the process and start anew.