(In no particular order.)

When writing:

• Which pieces of content would benefit from a graphical illustration?

When editing:

• Is the tense consistent?
• Is the usage of pronouns (you, we) consistent?
• Is the use of passive voice reasonable?
• Are the sentences short enough?
• Are the references up to date?

When reviewing:

• Separate into passes (in no particular order): content, spelling+grammar, formatting, punctuation.