Rule of thirds is a big one. The camera grid is the single most important tool to help frame a picture, always have it enabled. You can use cropping to fine-tune it later if needed, but the picture should have a decent starting point.

If you want to practice composition, use a static landscape. Static removes timing from the equation and the relative size difference between you and a landscape make adjustments (both in location and aiming) less sensitive.

Try doodling/sketching. Not necessarily as an end-goal to learn drawing, but to exercise your artistic skills in general. I've spent years drawing in class out of sheer boredom during my tertiary education, starting out as a complete neophyte. I didn't realize it at the time, but I trained my artistic vision in the process beyond just drawing, which is probably why I'm also good at taking pictures. Practice improves your artistic skills, regardless of medium.