Feel free to ask me for my language notes: Before we begin: Notes on English and the editing of papers, theses and related work. If you go through it with care, your writing will improve.
A little book that is much loved and held in great esteem 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.
I strongly recommend:
Butterfield, Jeremy (Editor) (2007). Oxford A-Z of English usage. OUP: New York.
Ritter, Robert M. (Adapter) (2005). New Hart’s rules: The handbook of style for writers and editors. OUP: New York.
We live in very exciting times. Authors and practitioners used to have rows of dictionaries, which they would need to refer to every few minutes.
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 online. One of the greatest is the Purdue University Online Writing Lab (OWL) (http://owl.english.purdue.edu). You will find almost everything you will ever need on English usage here.