Throwing kicks or knees can surprise your opponent in a street fight. If you are too far out of range to punch, kicking to the head can ko your adversary easily. Aim for the side of the head or even try to wrap your kick around the back of the head to drop your opponent. Knees can be devastating in close range, grab ahold of the back of the head and pull down as you knee to the chin.
With kicks you can afford to give up a little bit of precision and replace it with power, but again a clean strike to the chin or side of the head should take out an aggressor with ease. Another key aspect of good kicking or punching is keeping a good stance, as illustrated by the image below: