There is one thing I know for certain: You cannot learn everything by yourself.
Every writer can improve and hone their skills. I've taken classes in college and high school to learn more about grammar. References are a HUGE help and I've manage to come across a few books/tools to develop my skills. They're extremely useful and I hope you find them just as amazing as I did. These are not all of the resources I use but are some of the best.
I don't know any author who couldn't survive without a thesaurus. It doesn't matter if it is this one specifically, but you will need one; whether you use it via the web, book, or iphone app. There is always another way to phrase or describe a scene/person/thing. Using one word over, and over, and over is annoying. I will say it again. It is annoying. So please, invest and use a thesaurus, for your sake, as well as your future readers.
Now I know half of you don't have any interesting in writing romance and I know the other half do. Understand, this book is not just for romance. It has many, many different tips and tricks to create loveable characters, conflicts, and resolutions. It also includes some exercises and reviews of each chapter to guide you through each technique. The one thing I found extremely beneficial is the fact it contains examples of work by other authors. It's one thing to say do this, or do that, its another thing to show how you can apply the tips into your writing. This book has been a great help to me and I definitely recommend it for anyone wanting to upgrade their writing skills.
This is a superb book to help for settings and descriptions. The author has other books for plot/structure, characters/emotion/viewpoint, and dialogue. I love this book because of the excessive exercises and checklists for each section. There are a ton, and I mean, a ton of techniques to generate believable people, places, and events. Along with showing and teaching you different ways to use the advice, its also a guide to the "nuts-and-bolts" for writing a story.
Not only does the author of this book write resources, but she has many amazing series with unique names. One of the toughest decisions to make for a story is choosing the character names. Personally, I don't like common names (ie. Adam, Sam, and Clara.); instead, I'm open to a mass majority of unique names. Hands down, this book is awesome. It's filled to the brim with names from every culture imaginable and it contains surnames as well. Names from Czech, Maori, Polynesian, and Thai are all within this magical, wonderful reference. I don't know how I managed to survive without it before. Sure you can go online and find baby names, but this book has over 400 pages of names directly at your disposal you'll probably never be able to come across without searching for hours. This is one of the best books ever made. Thank you Sherrilyn.
I got this little treasure for a birthday present and let me just say, holy cow is it mind-blowing. I'm sure everyone's had writers block at some point in time. This book is all prompts, and mind you, not boring prompts, but funny, creative, and exciting ways to help you focus on writing and let your imagination continue to run wild. One of my favorite prompts is: Before all else, be armed - Niccolo Machiavelli. Doesn't sound familiar? Well, if you have ever played Assassins Creed Brotherhood, you should most certainly recognize it. This is a great tool and a way to have fun while practicing your skills.
This is probably one of the most expensive resources I've purchased because it was my college textbook. Mind you, I haven't really ever recommended a textbook before because they're costly, but if you manage to purchase a gently used version, I guarantee it'll be worth it. I'm a huge grammar freak and there is always one mistake everyone makes while writing. With this book, grammar, research/writing strategies, and writing/thinking activities are all present. It's a great resource to have if you need help with school or personal reasons. It has exercises and examples to help you understand what is good and what is bad. Undoubtedly, this textbook is well worth the money.