The most common issue with heelside turns is keeping legs too straight & bending at waist instead of squatting down with knees/ankles. Here is a good coaching video on proper heelside technique.
If you can post a video of your riding, people can give more detailed feedback.
A variation of the drill mentioned above is practicing straight-lining to a fast heelside brake. You will need to keep your chest upright and bend your knees and ankles to absorb the pressure. If your body position isn't good, you will chatter out and fall. It is a good way to get realtime feedback on body position without a camera.
Video going over the drill here:
If you can post a video of your riding, people can give more detailed feedback.
A variation of the drill mentioned above is practicing straight-lining to a fast heelside brake. You will need to keep your chest upright and bend your knees and ankles to absorb the pressure. If your body position isn't good, you will chatter out and fall. It is a good way to get realtime feedback on body position without a camera.
Video going over the drill here: