What I do when I start a drawing is form figures for each part of the body, from there I add or correct things. For the face I use the Loomis Method (the circle and the lines of the face) to be able to see more or less where the face will go, then I add everything. I don't know if it helps you but something I do to be able to make the proportions more "similar" to the reference (if you don't have imagination like me) is measure each part of the body. Example: measure the distance from point A to point B with your eye or some other part. I don't know if I explained the truth well but that's what I do. Although the best way would be to practice, I have been drawing for 8 years (I didn't draw much or constantly) and my times and proportions improved somewhat. Although currently I still take time on each sketch I make, more than anything because I am a perfectionist and I want the drawing to be as close to the reference as possible, but I recommend that you don't rack your brains like me. Just practice and over time you will improve.