Basically, here’s a guide:
1. Make sure your story is completed and well-edited before you even consider what to do with it.
Regardless of whether you plan to submit it to an agent for publication or to self-publish (vanity publish… which I don’t really recommend, because most of the industry frowns on the practise, seeing it as circumventing them/putting them out of a job & it’s very rare for a self-published author to make it big as a result — EL James was a fluke), it needs to be a clean, well-written copy. Typos, grammar issues, etc. will make you appear amateurish, and no one will be interested in reading your story.
In order to assure your story is solid, most aspiring authors join crit groups (i.e. groups of people who you trust who are well-read and literate, who share their stories with each other and offer advise on how to improve the writing). *Note: Make sure everyone in the group has agreed to non-disclosure and copyrights, or else you could risk your story being stolen and published by someone else (I have seen this happen).
2. Once your story is done, you need to multitask. Part of your time should be spent on creating a smart business plan (because as an author, you are a self-employed business, and as such, you have to understand how royalties work, how to read contracts & understand what rights your signing away, how to negotiate a good deal to keep rights to your work, how to report such earnings to the government, and how to run a business out of your home). The other part of you needs to split your remaining time between writing query letters to agents (if you plan to go that route)/prepping your story for self-publishing issues (if you plant to go that route - i.e. obtaining an ISBN, buying cover art, learning what online resources offer the best return on e-book sales vs. exposure to a larger audience, distribution methods, etc.) and move on to your next story immediately (because most publishing houses want you to have at least 1 in the hopper with 1 complete before they consider you).
Never go idle as a writer. Just because you’ve finished a story doesn’t mean it will sell. Always be prepared for it to flop or never get published, and write other stories to console yourself with the failures. They happen. Not everyone is going to like your ideas or how they are presented. Accept it, take it on the chin, and march on. Come up with new ideas all the time.
3. If you intend to get an agent, you have to send query letters to available agents in the genre you tend to write (i.e. romance, young adult, etc.). There are sites online that will allow you to know what agents are currently accepting new authors, and the genres they are accepting for publishing purposes (some agents are experts at certain fields, and some include lists of genres they WON’T publish this year, i.e. vampires, werewolves, etc.). Agents read these introductory letters, which includes a brief background about you and usually a catchy synopsis of your story. If they’re interested in reading more, they contact you. If the agent likes the work you send them, they will consider signing you and offer you a contract (the terms of which are negotiable).
Remember: the agent you pick is a doorway into publishing - they hook you up with an editor, who hooks you up with a publishing house (in a nutshell). The industry has changed a lot because of vanity publishing, but this is still the basic gist. PICK YOUR AGENT WISELY (be discerning). Don’t just jump at the first offer, and don’t pick an agent because they take you to dinner or are super nice to you. Look at who else uses them, who they represent, and how many contacts they have with the industry. Make sure what they can offer you is compatible to where you want to go as a writer (if you’re looking for a movie deal, find an agent with solid contacts in Hollywood, etc.). As a writer, whoever you choose to represent you will open some doors for you and close others (depending on who they’ve angered or annoyed in the industry previously). It’s all very political and unfortunately, blacklisting does exist, so you need to consider your choice of agent (and how to turn down other agents) VERY carefully.
*NOTE: I would also NEVER tell an agent you were/are in any way involved in fanfiction or fanart, no matter how excited you are about it. It’s considered a taboo subject by many of them because of the copyright issues. Bad idea. Trust me on this.
*Note: There are websites online dedicated to helping you know how to write a good query letter. I highly suggest you read as many as you can before you try to write one of these.
4. Once you have an agent, your business relationship with them will commence. There is an expectation of putting out at least 1 publishable work a year (some agents demand more). You have to gauge your audience, build up a fan base for demand, and assure you are hip on marketing techniques (as some pub houses have terrible cover artists). Early in my career, I didn’t understand such fine nuances, and some of my stories were pub’d with terrible cover art that I’m embarrassed to look at now, and which definitely affected sales (which affects how many copies a pub house prints or how much of a marketing budget they apply to you, which corresponds directly to how much money you make and whether or not you appear on a Best Sellers list… and whether they think you’re a name worth continuing to publish).
5. Attend writers conventions and join an association of writers in your genre in your area (i.e. The British Fantasy Society, Romance Writers of America, etc.). You need to network, because you need to have published authors willing to write a blurb for your book to help it make more sales (a blurb is something like, “BEST BOOK OF THE YEAR. Couldn’t put it down!” - Stephen King, or “A witty ride through Victorian England featuring steampunk zombies. The most imaginative plot I’ve ever come across!” - The British Fantasy Society, etc. - appears inside or on a cover, usually). Conventions also offer you a chance to do signings for fans, which is a great way to get the word out that you exist and recs from fans on sites like Tumblr (which can improve your image and sell books).
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*pant pant pant*
I think I covered the basics. I hope this help you. Good luck with your writing, dahling!!!