Here is a collection of guides, online and print, which are useful if you want to polish your grammar skills as a proofreader.
Grammar is often influenced by style, genre, and dialect, so bear this in mind when taking the advice of any grammar guide on board.
- English Grammar for Dummies, by Lesley Ward (angliciser) and Geraldine Woods, John Wiley, 2007
- Rediscover Grammar, 3rd edition, by David Crystal, Longman, 2004
- The Grammar Devotional: Daily Tips for Successful Writing from Grammar Girl, Mignon Fogarty