Whilst in many ways the Kick on Side drill is a very simple drill, it is also an extremely important one that should form part of a technique session for most, if not all, swimmers.
Wearing fins, push yourself off the wall and turn straight away onto your side, so you are effectively facing the pool wall. Your bottom arm should be outstretched in a straight line directly from your shoulders. Your other arm should be resting by your side. Keep your head down and just gently lift it when you need to breathe in.
Use this simple kicking drill to develop good alignment by positioning your arm straight out from your shoulder. If you feel your arm is crossing over, draw your shoulder blades back to improve your posture. Be mindful of what happens when you lift your head to breathe. If your arm starts to cross over, press down or move wide, then it is very likely this also happens in your full stroke.
Also use this drill to establish and practice a good catch position. Your outstretched arm should have fingertips slightly dipped below your wrist and your wrist below your elbow. Your palms should be facing downwards and your fingertips will probably be around 30cm below the water surface. Be careful not to dip your elbow and raise your hand towards the top of the water as this will "put on the brakes" and hinder your ability to push water behind you.
Kick on Side drill progresses into 6-1-6 and 6-3-6. It is also a useful drill to master before attempting the Broken Arrow drill.