All of us involved in marketing have to do some copywriting. Some of us have to do it all. There are many books and articles on how to improve your writing style, but few people can take in everything they have to say. I find the best way to improve is to read one of these every now and then, to choose one suggestion, and to try to incorporate that into your writing. That's why I'll point you towards a good copywriting article every few weeks here. Read it, and resolve to act on one idea which appeals to you.
So here we go then. Read 10 Secrets to More Magnetic Copy on Copyblogger, and take one any of the ideas there onboard. Improving your writing is easy to read about, but difficult to do. So approach the problem manageably.
Was that brief enough?