When playing rest strokes, I find that whenever I push down with my middle finger (m) my hand is forcibly raised upwards, and so when trying to play scales and passages my right hand isn't staying still but rather moving slightly, and so I'm prone to making mistakes and can't attain speed. How can I avoid this problem?
curve your fingers forward, (not naturally but opposite to your body, it should feel a bit uncomfortable) make sure your hand is straight and not at an angle. Unless you show video I can't help you much.
... <snip> Unless you show video I can't help you much.
Which hits the nail on the head.
Or much more detailed description of hand wrist position, stricking action etc all rather difficult, so a (moving) pic = 1000 words