For your written papers, we usually indicate a maximum number of words you are allowed to write. So, there is no need to squeeze in everything on one page. Use 12pt font Times New Roman (or equivalent size), leave 3cm margins on the right, and use 1.5 lines or double spacing. Make sure your heading levels can be distinguished from each other (it’s useful to number them) and make a reasonable not only of headings and sub-headings, but also of paragraphs to structure your text.
For writing clearly, I recommend William Zinsser’s On Writing Well, on questions of style, you can also consult E.B. White’s The Elements of Style as well as the Chicago Manual of Style. The LSE Writing for Research Blog also offers some useful recommendations and reflections.