The fact that you're asking about how to improve your writing is a fantastic first step. I think writing is the most undervalued skill in most professions. No matter what your job is, writing is part of it. That very much includes technical and scientific jobs. So kudos to you for even thinking about this skill--it's one that many people ignore.

The best book on writing that I have read is On Writing Well, by William Zinsser. It's short and very accessible. Zinsser does a great job of laying out why writing is so hard and how to tackle everything from fiction writing to non-fiction technical writing. You can finish the book in a weekend of leisurely reading and come back to it as often as you like.

Zinsser's main point, which I agree with wholeheartedly, is that great writing is really about great re-writing. Edit mercilessly, remove unnecessary words and phrases, and focus on getting your point across in a clear manner. Remove jargon wherever possible. If you take the time to re-read and re-write your work several times over, you can't help but create something better than you started with.