I am a devotee of Strunk and White’s The Elements of Style. For academic writing, you will need to follow the direction of your instructor. College and university undergraduate students generally adhere to Modern Language Association (MLA) or American Psychological Association (APA)style. When you are looking items up, try to use the reference book as a text as well; if you can understand why an item must be written a certain way, rather than simply copying a pattern, then you will absorb the principles of English grammar and be less reliant on a style manual. I always told my composition students, if you cannot explain to yourself the grammatical reason why you need a comma, then don’t use it. “When in doubt, leave it out.”
An interesting perspective on effective writing is Michael Harvey's The Nuts and Bolts of College Writing. It provides some excellent thoughts on clarity, avoiding what he calls the "pompous style." He makes great sense about avoiding many of the "traps" of poor writing such as overuse of the passive voice so that writers understand not only what to do but also why they should do it.
And one of the best parts is that, in addition to a printed copy, it's available online at http://nutsandbolts.washcoll.edu/
The Blair Handbook is the one I would recommend (2003). I am part of the editorial review board and I used it for years with my 1101/1102 kids.
APA/MLA have both software programs (students and teachers get special rates) to run your papers.
Of you are in college, your university/college is likely to have a writing center where you can "hire" an editor to help you go through with it.
It really depends on what, specifically, you need.
Elements of Style by William Strunk - Nice, general guidelines, particularly when composition is taught alongside literature.
Any MLA or APA reference guide will generally have a section on editing and proofreading.
You may also want to try some online sources. Purdue University has a pretty comprehensive grammar and usage site: http://owl.english.purdue.edu/
Another good website is http://www.grammarbook.com/
I recommend The Little, Brown Essential Handbook for Writers, 5ed, or Diana Hacker's A Pocket Style Manual.