A student made an appointment just to ask me how to get better at drawing. The answer is to make more drawings. The answer to every problem with a drawing is to make another drawing.
Now, let's get a little more nuanced. I'm not just saying Practise, although I am definitely saying Practise. I'm also saying, Make Your Practice Deliberate. "Deliberate practice" is a key phrase from the study of expertise. (See The Role of Deliberate Practice in the Acquisition of Expert Performance, by Ericsson, Krampe & Tesch-Romer, 1993.) It's not enough to keep doing the same thing over and over again. You need to seek specific advice on how to improve, then do it again . . . but better.
How can you get better at drawing? Make a drawing. Look at it. Identify one thing you could do better. If you can't spot something, ask someone else to tell you one thing you could do better. Make another drawing and try to do that thing better.
Repeat. For the rest of your life.
George Carlin told this story: Pablo Casals, he was a past master of the cello. He was the virtuoso in the 20th century. He was in his 90s and he was still practicing three hours a day, and one of his friends said to him, "Senor Casals, you are such a past master, a virtuoso of this instrument, everyone knows it and acknowledges it. Why do you practice three hours a day?" and he said, "Well, I'm beginning to notice some improvement."