Ooooohhh thats actually a hard one to answer. I actually spend a lot of time planning the pages. There are a lot of rules to creating those boxes. (also called panels) For example, you need to avoid gutter clashes and make sure each page is diverse enough and that the speech bubbles and the panels flow so the reader can read it in the proper order. If it helps, here are some links to some material that covers exactly that!
A good book to also check out would be “Making Comics” by Scott McCloud! It covers a lot of detail.