Apart from a good dictionary and thesaurus, I like to use and recommend the following references.
This provides plenty of practical examples without the jargon. It also gives you the “rules” of grammar and punctuation...plus their many exceptions.
Chicago Manual of Style
A trusted favourite by many, it can be a bit technical, but still a good reference to have.
Useful for British manuscripts or manuscripts which use, in part or whole, the UK language.
A Handbook to Literature (Harmon & Holman)
This is basically part dictionary/part encyclopedia of literary terms and styles.
I also like to recommend the following resources:
The “Write Great Fiction” Series – Writer’s Digest Books
There’s a reason so many authors recommend and use these books, and that’s because they are excellent.
Guide to Fiction Writing – Phyllis A. Whitney
“...when a writer’s work is in competition with all those thousands of other manuscripts that pour over an editor’s desk, he cannot afford to be ‘as good as’; he (or she) must be ‘better than.’”
Considering Whitney’s illustrious and prolific writing career, she knew what it took to be “better than.”
Plotting and Writing Suspense Fiction – Patricia Highsmith
Highsmith is honest about the difficulties she faced when writing her stories and offers practical advice in this short book.
How to Write a Mystery – Larry Beinhart
Perhaps one of the most entertaining and detailed “how-to” about the genre I have read.
Getting Into Character: Seven Secrets a Novelist Can Learn from Actors – Brandilyn Collins
People may pooh-pooh method acting, but there is a lot an author can learn from actors when it comes to characterization and motivation—something every character needs in order to interest the reader from start to finish.
The Story Engine: A Writer’s Guide (ebook) – Matt Shutt
If you are ever at a loss on how to make your characters more unique or you’ve written yourself into a corner, this is a fun way to fix it. You can pick and choose traits and situations from the many lists inside, or do it totally by random—with dice!