Welcome to APUG.
Your work is good. Learning more about composing can be done several ways. One way is to study art.
Another way would be to read these books:
Perception & Imaging, second edition, Richard D. Zakin, Focal Press 0-240-80466-X
Art and Visual Perception, 50th Anniversary Printing, The New Version, Rudolf Arnheim, University of California Press, 978-0-520-24383-S
Find a way that works for you. There is no best way.
By the way, square is good!