Other than shooting more (which I plan to do already), what would you suggest to improve my DP abilities?
Practice. Shoot stills, think about the composition, lighting, and story that the still tells BEFORE you press the button. Review those, see what works, what doesn't. As previously suggested, see if you can bring together a series of shots to tell a larger story.
Watch films, any of them. Pause on shots you find compelling and try to work out how they were lit. Try to consider what the image says, how the players are arranged, how the production design enhances the shot/sequence, and so on. Watch the same scene repeatedly and get a feel for the edits, the shot selection, how the camera moves (or doesn't), and what impact that all has on you as the viewer.
Look at art; study the compositions and the colors. What do they say to you? How do they make you feel?
Learn about color and the various psychological interpretations of various tones.
Edit relentlessly, even if it's just for practice. Learn to properly expose an image, don't just rely on the in-camera tools for exposure (they like to lie sometimes). Experiment with reckless abandon.
Watch the world around you; how people move, behave, how light plays against texture, how motion contrasts with stillness.
Always be looking.