Practicing is one of the key aspects of improving your drawing skills. The core skill for me that needs practice is drawing cylinders. I like to practice using repetition. Notice in the sketch above, I started on the left and sketched cylinder shapes multiple times of different objects. One of the technique that I like to use when drawing cylinders, is to use a pencil line down the middle with horizontal lines placed proportionately down the object for both the width and height of each section. Below is an illustration from my perspective book on cylinder drawing with a center-line technique.
Found a great article on the Learning to See blog focused on how to practice drawing effectively. In a blog article Paul identifies the three critical steps for effective practice:
Be sure to check out this blog site: Learning To See – Inspiration and practical advice for aspiring realist artists.