Stuff I do:
- Spelling/grammar edits
- Removing superfluous content
- Updating/verifying references
Stuff I rarely do:
- Adding content (I usually either rewrite text or leave it as is and post a question in the article's talk section, unless it is absolutely necessary/appropriate to change it myself)
- Removing vandalism (by manually/auto reverting to the most recent, unvandalised version of the article)
- Polishing writing (i.e. present tense to past tense, when appropriate)