Make it your everyday practice to never let someone sneak up on you.
As humans, we are probably the most unaware creatures on earth when it
comes to survival awareness. To prove this to yourself, pick a busy
street, stand on the sidewalk, and observe the people walking by. What
you'll probably notice is that only about 1 out of 10 will be observing you
back.
One good thing about the scumbags of this world is that they are
inherently lazy, and don't want a challenge. They are looking for
someone who's distracted or unaware. In other words, someone who is easy
to sneak up on and catch by surprise. Unfortunately, that's about 90% of
the people in society.
Be one of the 10% who's aware of your surroundings and you'll be 90%
less likely to become that dirt-bags next target.