One of my earliest recollections of riding lessons, at the tender age of 4 or 5, was having “UP, DOWN, UP, DOWN” shouted at me as I tried to master rising trot.
Just rising forward a tiny bit is a much better bet, it looks far tidier and lets you control the horse’s rhythm better. If you then want the horse to do bigger strides in lengthened or medium, you can try doing bigger rises to encourage the stride to open.
Something my trainer says which I always find helpful is “Let the horse rise you”… i.e. don’t make an effort to rise, just let the horse’s movement push you forwards/upwards a little.