Rule of Thirds
The Rule of Thirds is a composition tool that most photographers use, It's an overlay consisting of a 3x3 grid. It's purpose is to help the artist balance their image so that helps draw the viewers attention to different points. Viewers shouldn't see the grid.
High Contrast
Contrast is difference and when something is different, naturally you are drawn to look at it or investigate further.
This is mostly common with light and dark, rough and smooth, red and blue, etc.

© Marjorie Sarnat. Original line art illustration is from Creative Cats.
Movement
Movement refers to how the eye travels over a design so you can have flow and direction over what is seen and what order it's in.
In the image, the waves have a natural curve upwards so your eye goes from the bottom, to the left, to the top where you see the rest of the painting.

© Katsushika Hokusai. The Great Wave.
Overdoing
As a designer, it's not uncommon to have plenty of vivid ideas, but it's easy to overachive, and have way to much going on at once.
When it gets like this, it's hard to comprend the aesthetic.
Step back and remind yourself what needs to be seen, and the message you're trying to convey.