In this video I show an important transition from Side Control to Mount. I primarily do this when I see the person place the foot on the knee in an attempt to prevent the mount (or crowd the space by hips). This is a great option and works both in the gi and no gi. Just make sure that you relocate your whole body and push with your shoulder and core rather than just the muscles in your arm. One of the only other important parts is stepping your foot onto the thigh rather beside the thigh. This will really make it easy for you to mount and difficult for your opponent to put you into guard.