You can improve by observing real-life objects and people to understand shapes and forms better. Another tip is to look at the works of professional artists and analyze their techniques.
To improve, keep a sketchbook and draw regularly. Draw from life as much as possible, whether it's people on the street or objects in your room. This will train your eye and hand coordination. Also, study the works of great comic and graphic novel artists. Analyze how they use composition, color, and storytelling in their art. Try to replicate some of their techniques in your own work to learn from them.
To improve manga drawing skills, start by copying your favorite manga panels. Analyze the line work, proportions, and expressions. Also, take online courses or attend workshops to learn from professionals.
To improve for Manga Vol. 6, start by analyzing the styles and techniques used in previous volumes. Focus on details like expressions and backgrounds. Experiment with different tools and shading methods.
Practice regularly. Just like any other skill, the more you draw, the better you'll get. You can start with simple sketches like drawing basic shapes and then gradually move on to more complex objects.