Mechanics Issues
Punctuation -
Reading your paper out loud, exactly as written will help you discover punctuation problems. Check each mark - is it necessary, is it correct? Watch for quotation mark changes in blocked quotes. Avoid exclamation marks for the most part in non-fiction prose. Check reference guides for accuracy - don't assume it will just 'look wrong'.
Capitalization -
Review style guidelines, if any, where usage is dictated by teacher or publisher's preference. Review pronouns that refer to God - be consistent. Check sacred terms like 'Blessed Sacrament' and 'Real Presence' for caps. 'Satan' is a proper noun; you do him no honor to capitalize his name. Don't SHOUT at readers with capitals.
Spelling -
Spell checkers will not catch homonyms (write, right; lead, led; to, too, two; there, their, they're) or words that are spelled correctly, but have no business being used. Use a dictionary if you aren't sure.
Format -
Use an outline format to check consistency of headers, sub-headers, sub-sub-headers. Don't be a font fanatic - just because you can use lots of different fonts easily is no excuse to do so. Check block quotes for consistency of indentation. It's easy to hit 'tab' twice and indent the whole thing too far without noticing. Use the footnote style dictated for you, or stay consistent if you make the choice. Proof footnotes in a separate step and make sure the note falls on the page where the number appears. If your computer isn't automatically tracking footnote number changes, be especially careful to check this. The removal of a footnoted sentence or quotation will mess up your numbering.
Identification -
Don't forget to center your name under your title on the first page. Use a header with your last name, or title/last name/automatic page number after the first page. Pages submitted for editing should be unbound, unstapled for the editor's convenience. Loose pages are easily lost or shuffled, so identification is especially important.