I used to struggle with this too hun.
Some tips I read that really helped me a lot. I think were from Samantha Sweet,
to
Make sure you either sweep or see-saw on both sides, don't do a different way on each side, for instance I used to see-saw file on the right side of the free edge, then would swipe on the left side of the edge, as it felt a more unnatural side to do as I am right handed...
(practice now in the air, you will see what I mean lol)
and also, Keep your elbow tucked into your waist on both sides of the free edge....I used to keep my elbow tucked in to do the right side while see-sawing the file....then my elbow would stick out in the air when I was swiping the other side of the free edge...
These steps should help you along with the tutorial link there :hug: