A teacher recommended this book to me last semester. My initial
reaction was "what does he take me for, I can write very well thank
you very much". But after reading it, I realized how bad my writing
was - is.
The first half of the book is a general outlook on writing (style,
introduction, do's and don't's, etc.) Then it continues with a more
specific approach (art review, travel article, sports article,
etc.) which you can read or skip depending on what you're looking
for.
"On Writing Well" sounds boring, but the author manages to insert
such funny examples that you'll find yourself smiling throughout
the book. And best of all, it's a very easy read.