Whether you plan to submit your writing to a publisher or agent or to publish it yourself, you need to know how to line edit your work. That goes beyond basics such as correct spelling and grammar. For your writing to be clear and strong, you'll need to use active voice most of the time, avoid repeating the same words, and replace weak verbs with strong ones, among other things.
Self-Editing for Fiction Writers is the best book I've ever read on how to review and edit your own writing to make it shine. It's easy to read and easy to apply the points the authors make.
Have a peaceful, wonderful weekend (and holiday if you're celebrating one).
L. M. Lilly
P.S. Even if you plan to hire an editor and proofreader to review your manuscript, you still need to know what a properly edited piece of fiction looks like. If you don't, you'll run the risk of paying a significant amount to a poor editor, only to find out after you hit publish and see reader reviews that your novel is filled with typos and grammar mistakes.