The prerequisite for good mathematical writing is good English style.My favorite manual of style is available on line
http://www.bartleby.com/141/. This book, The Elements of Style, by Strunk and White, contains not only the rules of correct grammar but savvy advice about direct writing.
This English 126 sitewritten by Daniel Kies of the College Dupage has two notable features: a terriffic group of links to style sheets and grammar references (clear at the end of the site) and an interesting review of grammar checking by the leading commerical grammar checkers. Theanalysis shows that such grammar checking may help but too many errors are missed for anyone to rely on it. My impression is that the grammar checkers are helpful with small carelesserrors but miss serious structural problems. However, study of this site may be useful to identify and correct grammatical errors.
The preferred language for writing mathematics is TeX. At http://www.tug.org/interest.html you can find a description of TeX and sites to obtain it either as freeware or shareware or payware. It is available in the university laboratories. We will discuss in class the benefits and disadvantages of TeX versus `what you see is all you get’.[1]