Scrivener is a word-processing app designed with the novelist in mind. It organizes by scenes and chapters, it includes word count targets, outlining, distraction-free composition mode, corkboards, notes and comments, templates for brainstorming character and setting traits, and functionality for storing and organzing your research. It compiles to a variety of formats and there are templates people have designed to get you started with different genres and outlining styles. It is the complete package. Microsoft Word remains the standard for editing and beta reading especially because of its Track Changes functionality. If you can swing it, I recommend having both.
You can set aside your index cards because the future is now and there are a number of apps to help you plot your story. Three examples are Story Planner, Plottr, and Plot Factory. It helps to know the theory first and for that there are books, so many books. Try Story Engineering *, Save the Cat!*, How to Write a Damn Good Thriller*, and The Story Grid*. In terms of free resources, you can't beat the thorough advice from K.M. Weiland at her site Helping Writers Become Authors.
After you've raked through your manuscript so many times that you've committed it to memory, it may be time to call in a third-party tool to help you see your words afresh. ProWritingAid is editing software with a variety of compatible sources including Word and Scrivener. It will mark spelling, grammar, and style issues including vagueness, repetitiveness, and passive voice. While software will certainly pinpoint issues, nothing compares with the advice you get from other writers. That's where the writers' group comes in. If you don't belong to a local group, consider joining one or more online. Inked Voices offers writers groups for all genres and for all types of support whether simply accountability all the way through beta reading.
There is always more to learn and there are masters out there to learn from. Coursera offers a number of creative writing programs. I especially recommend Wesleyan University's Creative Writing specialization which covers plot, characters, setting, and style. It can be audited for free. On the spendier side, MasterClass offers a roster of greats ready to share what they know in high-quality video. As you establish your professional writing life consider joining The Author's Guild. This mighty fine organization offers online events and a plethora of resources to help you navigate the business of being an author. Even if you don't join yet, consider signing up for their newsletter which alerts you to their many free informative classes.
The query letter is a genre unto itself. To steep yourself in the snarky corrections of The Query Shark. Nathan Bransford also offers excellent advice. If you prefer your advice in video format delivered with a British accent, try Jericho Writers. Once you've written your query letter, you are going to want to track its progress. Excel works, but Query Tracker excels. Consider applying for Pitch Wars and joining a Twitter-based #pitmad event. These events get you insight into how other authors distill the essence of their book into a pithy pitch.
If you are headed along the self-publishing route, here is where you'll encounter some serious upfront costs. If you use macOS, Vellum is the way to easily generate typeset files for both print and ebooks. You may want to apply for a US copyright. Many publishers and distributors will require an ISBN. In the US, these are purchased from Bowker. Beware, the prices get much cheaper the more ISBNs you buy at one time.
In these internet-enabled times, it is vital to eek out space on the virtual shelves of booksellers. Choosing the right keywords and categories is the equivalent of moving from the back corner of the bookstore to a center display. Publisher Rocket is a desktop tool to help you select keywords and categories by finding search terms shoppers have used and assessing the competition for those word. It is backed by data from Amazon, but the keywords can be used across all platforms and it works for both books and ebooks. Once readers have found your book, you need to seal the deal with an enticing blurb. Reedsy walks you through the steps to nail it.
Facebook, Bookbub, and Amazon ads present the opportunity for you to adverties in the same places as the big publishers. The only problem is knowing how to run a campaign. This is a career in and of itself, but I'll point you to the resouces of David Gaughran to get you started. From his website, you can find links to his collection of tutorial ebooks, his blog, and his videos, and sign up for his newsletter. Absorb his tips to learn how to get your book in front of readers.