I recommend reading and practicing composition rules. Here is a very good guide on the subject.

There are different rules for objects, landscapes, and portraits. In general, they include the rule of thirds, leading lines, vanishing points, negative space, and the golden rule (which I personally find the hardest to compose). Knowing the rules allows you to explore new possibilities for the same subject and to notice things you wouldn’t have seen before.

Improvement comes with practice — keep photographing.

Note: Don’t get stuck on the rules or stop taking photos just because you can’t apply them. A good photo isn’t defined solely by that.