Grammar Gremlins: Taming the Mischief-Makers of the English Language by Don K. Ferguson
If you're smart enough to understand the importance of language skills (and have identified some mistakes in the first paragraph even if you don't know the rules that govern them), but have been waiting for a book that makes spelling and grammar simple, wait no more! Grammar Gremlins gives you the information you need in an easy-to-use format that's fun to read.
Used hardcover in dust jacket, minor wear, binding tight, light spotting to pages, a nice copy.