A little book that is much loved and held in great esteem (by most) is William Strunk and E.B. White’s The elements of style (now in an illustrated edition!). Bear in mind that it addresses U.S. English only. Further, I strongly recommend:
We live in very exciting times. Authors and practitioners used to have rows of dictionaries, which they would need to refer to often.
Among others, we now have Word, with its language preferences, Spelling and Grammar function, Track Changes function and Search/Find function. We also have search engines. These tools are very powerful and right at our fingertips. We have reason to be grateful for them. Please use them, and use them well.
The best language resources are available to us online. One I strongly recommend is the Purdue University Online Writing Lab (OWL) (http://owl.english.purdue.edu). You will find much of what you could need on English usage here.