I'm sure by now you've read Strunk and White.  It is, after all, only 80+ pages.  I'm sure any writer, regardless of experience, would agree that the information in that small book is invaluable.  Strunk (and later edited and updated by White) offers many of the basics that seem to slip between the cracks of life as time distances you from high school and Freshman English classes. As far as craft goes, however, it is a bit light.  In spite of that, every writer should read it and then re-read it several years later.  It's like adding booster to your engine.

Strunk is quite opinionated though.  He admits that some of his critiques on style are debatable, but if you follow his words, there is safety.  After reading this book, I was more aware of my writing.  The advice there in is crucial when rewriting, even if you debate about some of the more stylistic pet peeves like "student body" vs. "studentry."

White's short chapter on craft and usage is concise and emphasizes simplicity in writing.  He bolsters Strunk in everything and admonishes the need to cut unnecessary words.

If you haven't read it yet, do so.  It, at times, feels a bit tedious, but you will be grateful to have read it and your writing will be that much stronger.