In the past, my writing has been good enough to get the job done for classes. However, I would like to learn to write in a way that is enjoyable to read. I know that the usual advice is to read and write more often, but I was hoping that HN would have some book suggestions to improve my prose.
On Writing by Stephen King is quite good. Depending on where you'll be writing, Content Strategy for the Web by Kristina Halvorson might be useful, too.
A great suggestion. And I'll second King's own suggestion to read The Elements of Style by Strunk and White. Though, some of its advice might be a bit dated and best used in small doses. But to will provide a great foundation.
The best book on understanding what style means: Clear and Simple as the Truth. Every other book just has confusing "this is The Correct Way", which is wrong, it all depends.
Once you understand style, either try for style they mostly talk about in that book (classical style), or if you want practical style then Revising Prose or Style: Toward Clarity and Grace are good.