Criminals generally tend to look out for people who are not on their gaurd, particularly women.
Always be aware of your surroundings... when I am listening to music I will always have one ear free.
Make sure your purse is not easily obtainable. When I have particularly large amounts of money I will keep my purse tucked tightly between my arm and my body (think about keeping money in your bra).
It is best to avoid conflict with a man (or should I say a cowardly man) but if a situation happens to arise you will most likely not be able to beat him with strength alone.
Your elbow is the strongest point of your body... use it.
Pinch the area between the armpit and the elbow as hard as you possibly can, use no restraint. A woman once before tore out muscle strands from a man's arm doing this. I personally have tried this on my brother with very light pressure and he yelped and jumped away.
If you kick a man in his private parts as hard as possible... it will hurt. This will not neccesarily disable him so stay on your guard.
Use this last one as a last resort if he really intends to hurt you because you could cripple him doing this... kick him in the knee.
Pop him as hard as you can in the knee cap with your heel, he will crumble. You could also kick his knee from the side... but you have to do these very hard.
I'm not telling you to seek out this guy and do what I just told you, these are for self-defense, if you are ever in a situation where a man is trying to hurt you.