First of all, I have to say that the way you train is the way you will react. A plan is better than none at all. Don't plan to stand and fight. Make your plan be to get away. MY friends may call me Big_E but at 5'7 I'm really not that big. I'd rather run than stand and fight.
Carry a can of HALT. It works on people just as good as animals. The cans are cheap so you can go in your backyard and spray a can at a post or rock just to see how to use it, just go ahead and waste a can.
Keep a can clipped to your bike or backpack strap and practice whipping it out and aiming it. I do this twice before I had off to work each mornings but I prepare for those darned dogs that chase every mornings.
Casually watch your surroundings as you ride. Avoid riding too close to groups of guys, especially if they appear to be up to no good. As a bicyclist you'll be in better shape than most assailants so just use your common sense and see whats around you at stops signs and stop lights.
Keep a cellphone on your person. My cellphone is almost a part of me.
Thats all for now.