I think a good way to improve your writing is by reading lots of good and quality articles. Then, your writing will improve naturally.
http://search.barnesandnoble.com/If-You-Can-Talk-You-Can-Write/Joel-Saltzman/e/9780446395076/?itm=4 One of the best books I've read. Start there, and keep at it.
As many have said, there's no easy way. It takes practice, practice and more practice. Read as much as you can, but be selective in what you read. The internet is littered with badly written articles so stick to mainstream press/news websites or hardcopy books, newspapers and magazines. Write something, anything, whenever the notion comes upon you. Read every word you write, but not immediately after you've written it. Have a look at the site in my signature for more tips. The sitemap will give ready access as well.