Here's an interesting look at the evolution of a cover: The original version of Classic X-Men #1 by Art Adams.
The prelim sketch below was credited to John Romita. Was he teaching Art how to tighten up his layout?
Below is Adams' second prelim, based on John Romita's poses, perhaps.
And here we have the final Classic cover!
Along with a recolored version.
Finally, we have a recent commission showing how Adams would attack this composition today!
Most of the images come from Marvel Comics of the 1980s: