The biggest thing to do for self defense is in the mind.
First, learn and practice situational awareness.
Second, using the first avoid situations that will lead to problems.
Third, if you can't avoid it then try to talk your way out of it and then leave.
Fourth, if talking doesn't work then have a firm mindset that someone is going to die, you or the other one.
Fifth, learn enough of some technique so that you are confident you can make the other one die. (This confidence shows in body language which goes a long way towards making others not start a problem to begin with)
Sixth, develop a high level of physical fitness so that you can effectively use whatever defense technique you learn. (This includes both strength and aerobic fitness and also allows you to naturally project mind beams that tell others you are not a victim)
Conform and be dull. —James Frank Dobie, The Voice of the Coyote