The memo: text layout
The default margin settings on your word processor are probably one-inch margins at the top and bottom and one-inch margins on the left and right. These settings are fine for the traditional legal memo, and you can use them unless those you work for tell you to change them.
The typeface probably defaults to Times New Roman, 12-point, and this is also acceptable for the legal memo.
Your line-spacing default will be single-spacing, but most legal memos are double-spaced. Double-spacing leaves room for the reader to write notes between lines, but it also uses up twice as much paper or takes twice as long to scroll through on the screen. It also makes it difficult to skim the document. Still, double-spacing is a tradition in legal writing.
If your supervisor allows you to use a modern approach, try a single-spaced document with larger type and larger margins: 13-point type with 1.3-inch margins.
You will need to choose between underlining and italics for parts of your legal citations, and I strongly recommend italics. Underlining is what we used to do when we used typewriters because typewriters couldn't do italics. You will also need to choose between ALL-CAPS and boldface for emphasis; this is usually for headings. Here again, you have a choice between what we used to do on typewriters (ALL-CAPS) and the modern printing practice (boldface). I recommend boldface.