There is nothing that you “shouldn’t” do in my opinion. The creator is free to use whatever style or composition he/she wants.
However, though the creator has this freedom, it’s necessary for them to consider how the readers will feel upon reading their work…
Does the story have characters that the readers will like?
Is it easy to follow the flow of paneling?
Such questions concerning the reader are necessary when creating manga. This why the most difficult part in creating a first chapter is introducing the protagonist of the story, showing the world and how it works, as well as a clear and understandable plot. Everything has to catch the attention of the reader and make them turn the page.
As such, if we keep these “what needs to be done” points in mind when creating a manga, the creator should naturally find the “what shouldn’t be done” points disappear one by one.
Thank you.Keitaro Yokoyama