When you've spent hours and hours reporting and writing an article, it's inevitable that you'll lose a certain perspective on the writing: you've seen these sentences and paragraphs so many times that structure, repetition, and organization become harder to keep track of. In large part it's the editor's job to make sure your article makes sense, but if your writing is strong to begin with, the final product will be that much stronger (and your editor will love you more).
Some of the simplest things you can do to make your life and your editors' lives easier include: Using your computer's spell check before you send a draft to your editor; watching your use of the passive voice; and reading either Strunk and White's "Elements of Style," or Arthur Plotnik's more contemporary take, "Spunk and Bite."
The University of Minnesota's Center for Writing offers section on common grammar errors, active vs. passive voice, colons and semicolons, commas, hyphens and quotes.
The Columbia Journalism Review's Language Corner offers easy-to-read discussions of some of the most difficult grammar topics in the English language:
http://www.cjr.org/tools/lc/
Also be sure to familiarize yourself with the Associated Press Stylebook and the Chicago Manual of Style. Each publication you write for will use a version of one of these styles, so the more you know about them, the better. WireTap uses Associated Press Stylebook.