Originally from Riclin Firearm Training:

You can increase your awareness by looking for specific things as you go about your day-to-day activities. For example, when going shopping make a "game" of spotting as many tall, dark haired men with a moustache as you can. Next time look for something else. Remember also that "playing" awareness games makes you appear more observant and aware to a predator who may be evaluating you as a potential target and who may decide to look elsewhere because of your awareness.