Read what is actually on the page, not what you think is there.
Use a spellchecker, but don’t depend on it.
Have others read it.
Give a copy of the document to another person and keep a copy yourself. Take turns reading it out loud to each other. While one of you reads, the other one follows along to catch any errors and awkward-sounding phrases. This method also works well when proofing numbers and codes.
Point with your finger to read one word at a time.
Don’t proof for every type of mistake at once. Do a proof for spelling, grammar, consistency of word usage, font sizes, etc.
Keep a list of errors you tend to make and doublecheck for those.
If you are editing within MS Word, use the “track changes” tool to make your changes apparent to other reviewers (additions and deletions can be set to appear in different colors).
Print it out and read it.
Pay special attention to proofreading the headings. Headings are prone to error because proofreaders often don’t focus on them.
Double check fonts that are unusual (italic, bold, or otherwise different).
Be careful that your eyes don’t skip from one error to the next obvious error, missing subtle errors in between.
Double check proper names.
Doublecheck boilerplate language, such as EEO statements, department statements, etc.
Review page numbers, table of content and footer/header material for accuracy and correct order.