lunge from one leg and kick with the other. If its possible try and through ur weight with the kick, so as to make more of an impact, but be carefull if u miss the oponent. Its also a fairly easy attack to dodge or turn against u(as in, if someone catches u what do u think the first thing they will kick will be).
Here I will teach you one of the most effective ways for a side kick taught in TAE Kwon do, Karate, and Kung fu. 1. From a front ready stance, move your front foot outward 90 degrees ( some people do 45 then do 90 as they kick, but that is harder to balance) 2. Bring your knee straight up as high as you can 3. Kind of Twist your raised knee leg so that you can extend sideways and kick with heel of foot. We are taught this way as taught in many karate, use your heel edge. The chambere of your foot is littles toes bent down Big Toe up to protect your foot. One of the most powerful ground kicks next to the back kick. If you train these steps every day doding it will be hard, since you will have much higher flexibility and speed. as well as range.
Whatever you do, do NOT bend your body back to gain more stability or to kick higher, you will loose lots of power and be very vurnerable. Keeping your body upright , you will be able to use your bodies weight AND the kick against them. Ever see Bruce Lee do a Side kick, he does it right.