Always double space - whether text, displayed quotations, endnotes, footnotes, references, or bibliography. Always stop well below the bottom of the page, to avoid xeroxing omissions. When editorial revisions are made, please type alterations above the line of text, not in the margins - don't write them in by hand unless the change is minor. Hand in the top copy of your MS, plus two others. For the same reason, don't print out with proportional spacing.
Footnotes Try to avoid footnotes - they are very tedious for editors and typesetters.
Some people do not find this easy. Here are a few hints. Insert brief references in the text. Revise text to include 'asides'. Cut out parenthetical allusions altogether.