I won't tell a faceless man over the internet how to kill somebody, however, here are some things I can say:
In street fights, people tend to shove or punch the face. Keep you head guarded, because your brain is in there! Your brain is your most powerful weapon. Since people go for high targets, stomp on feet, and kick above and slightly to the left on the knee. It won't damage the person, but it will stun them and make them feel like their leg is broken.
If someone tries to kick you with a high kick, smash their foot with your elbow.
ALWAYS SCREAM. Even if you are defending yourself and the person is on the defensive, yell "Stop hitting me!" in case witnesses are around.