I have done a little research on the body language that we should be careful not to exhibit.
Walking with your eyes downcast: There are a lot of people that due to the emotions of depression, loneliness, sadness, and etc. Will walk with their eyes towards the ground with realizing it. This shows the predator that they are not paying attention to their surroundings and will be easier prey because of it.
Walking with arms and legs out of sync: In the military some of the first things that were pounded into us was that we had to walk with a certain form of balance. I found it impossible to do otherwise, but there were members of my squadron that just couldn't coordinate their bodies and would walk without a certain balance. Go for a walk and you will see that it is difficult to walk without taking a step with your right leg and moving your left arm to a forward position to stabalize you. If you walk so that arm moves with the same side as the leg.. right leg and right arm move forward.. or walk so that only your legs move and not your arms, you've labeled yourself as a target because you are destracted and are having intense emotional turmoil which makes you vulnerable.
Bumping into people: This isn't so much body language as just not paying attention. If you are on a busy street and you bump into a lot of people or require them to take large steps, a predator will take notice and label you as potential prey.
If you are playing with something in your hands.. You hair, your keys, your mustache, a coin, a ball... whatever.. These are indications of destraction. Again, potential prey material.
The best way to walk is to hold your head up with your chest out. Pretend as if you are a puppet with a string attached to the top of your head pulling you up.. not up so much that your feet leave the ground, but enough so that your back is straight and your shoulders are back. Look around and be aware of things. If you are being followed, turn and look at the person following you. Let him know that you know he is there. If you are stopped, appear confident, friendly, and polite. Be respectful no matter what. If he or she shouts and curses at you, keep being respectful. Don't raise your voice. If he/she wants to listen, they will. If not, then you raising your voice isn't going to do anything for you. Conserve your energy for when a strike is thrown. Stand with your hands at your side or one arm across your stomach and the other on your face (like you are feeling your beard), which is a passive type of guard.. Or if they are yelling at you put your hands up to shoulder level as if holding your hands up in surrender as you take steps backwards. This makes the bully feel as if he has already won and might leave you alone... but it also puts your hands up ready to defend yourself. Never fold your arms or put your hands behind your back or in your pockets. Don't stare him in the eyes. I don't say that because he will take that as a threat but because if you focus on looking him in the eyes, he might have a friend sneaking around behind you.
Move! Angles are preferable to backwards because there is a good chance you will trip if you move backwards. But if he advances you need to move. Its a whole lot easier to move yourself than it is to move him. If he grabs your shirt, let him. If someone grabs you its a good thing. Why? Because you know where one of his weapons is. If he has his hand on your shirt or arm, then you know that he's not going to punch with it. He probably won't kick with that side because he will have to remove his hand in order to get the most power and you can always just tug on his hand and force him to plant weight on that side to nullify the kick. If he goes to strike you with the other hand you can use the same motion to pull and force the other arm to go back a little bit which will reduce the power of the strike. So, if he has grabbed you, leave the hand there.. this is adequet reason to strike back, but you want that hand there. Now if he starts pushing or pulling you, that changes things and you begin to act. Practice this blindfolded. Have someone grab your lapel or arm and then throw a punch with their other hand. S..l..o..w..l..y at first. You will be able to feel the shift of weight that comes with the strike and be ready for it.
Above all, avoid situations where any of this information might be needed. Find a bar where the patrons don't tend to get rowdy. (like will attract like, people looking for fights will go where fights are known to occur) Go the long way around to avoid areas where the criminal element lurks. If you must go there, go there with someone else. Keep alert too. Use your common sense, primarily.