How you write affects how you are understood. Fonts provide one key to easier understanding by your audience, whether it is a judge, law clerk, or mediator. The number one rule: use fonts with serifs for the main text. Serifs are the horizontal lines at the top and bottom of letters. They include Times, Garamond, New Century Schoolbook and others. Testing shows they are easier to read; attention strays less with such fonts.
Perhaps the best source for advice — Typography for Lawyers, 2nd edition, by Matthew Butterick. That book is worth ten times its price,and is available on Amazon.