A couple of points to remember for the knots your tying.
First with the heavier line, don't make a lot of wraps. 5-7 does just great with the knots. Make sure when you pull the line that you dont pull really fast and the end of the line isn't straight up when doing it.
Hold it perpendicular to the main leader and pull on the hook with the end of the leader. I used to have the same problems many years ago and these simple points made all the difference.