what I'm still having a hard time understanding is as to why you can't have to strong elements in a shot competing.... My initial idea (although not successful) was to create a conflict between the 2 subjects (tree vs. cloud) to keep the eye going back and forward..
There's been a lot of water under this old bridge since art in college, but there's a thing called "Balance" in art. It refers to the sense of how we perceive visual weights that offset one another, IE- your tree and the sky. Additionally, elements should be arranged to have either symmetrical balance (equal on each side), or asymmetrically (different but arranged in a way they feel balanced). The rule of thirds, Fibonacci's ratio, etc., seek to guide you towards that end.
When you have two strong elements with a weight difference in the two, it allows the eye to be drawn to the stronger of the elements and find a resting place. Assuming other things like color harmony, contrast, arrangement of the elements, etc., are in alignment, then the composition seems to be "in balance" making the viewer feel more comfortable, hence a more pleasing image and one which the viewer lingers on. Imbalance causes an unsettled feeling, the viewer isn't likely to view the image for very long, nor will they like it.
As the artist, it is your choice to determine the direction you want your image to take. However before you seek to break the rules, you should probably study them in more detail, so that you have an understanding of how your viewer will perceive your image. There are those artists out there that deliberately create imbalance to disturb the viewer. Some may like it, but myself I don't care for it, and generally move away from it quickly. Course that may be the OCD side of me kicking in