The easiest way of putting it is that the image scale (=magnification ratio i.e the object size to the size of the image on the sensor/film) AND the aperture determine the depth of field. No more, no less. Wider angle = more depth of field (for a...
If I have an image that I like, but the crop doesn't seem obvious, I usually start as @brett8883 mentions and use established rules of composition, but I won't hesitate to deviate from those norms if my eyes tell me otherwise.
I can see your...