Trying to improve my pencil drawing. I think my biggest needs are speed and getting proportions correct. Any ideas for some exercises that will help?

About a year and a half ago, I tried making a diamond painting for the first time, together with my grandma, as an attempt at keeping her occupied. Since then, she and some of my other family members have gifted me several others to make, because I said it was fun to do. The problem is, each sing...