To be a freelance writer, you need a good dictionary. You need a decent thesaurus. And you need a few of the following.
Writers’ Reference Books
Writers’ and Artists’ Yearbook 2023 — for UK
The Writer’s Market 100th Edition — for US
The Writer’s and Artists’ Yearbook Guide to Self Publishing (UK)
Grammar / Punctuation / Spelling Books
Oxford A-Z of Grammar and Punctuation
Collins Improve Your Grammar
English Grammar for Dummies
Improve Your Punctuation and Grammar
Collins Improve Your Punctuation
First Aid in Spelling
Books about Words
Mind the Gaffe
Troublesome Words
Oxford Dictionary of Word Origins
Oxford Dictionary of Quotations
Oxford Dictionary of English Idioms
The Reader’s Digest Reverse Dictionary
Freelance Writing Books
No Contacts? No Problem! — Catherine Quinn
The Renegade Writer — Linda Formichelli & Diana Burrell
How to Make Money from Travel Writing — Sarah Woods
Writing Guides
Wannabe a Writer? — Jane Wenham Jones
The Writer’s ABC Checklist — Lorraine Mace & Maureen Vincent-Northam
The Positively Productive Writer — Simon Whaley
50 Mistakes Beginner Writers Make — Alex Gazzola
50 More Mistakes Beginner Writers Make — Alex Gazzola
50 Mistakes Writers Make — Alex Gazzola
Miscellaneous Books for Writers
On Writing: a Memoir of the Craft — Stephen King
Photography for Writers — Simon Whaley