This post is pretty general. I'm not breaking new ground, here. Later I’m going to get much more specific (How do I format the chapter headings on the print version pages? How do I manage page numbering? What’s the right indent for paragraphs? How do I format for Kindle or iBook? That kind of thing.) But I ought to start with a few notes about the writing part.
If you spend a little time searching for advice on getting published, you’ll see lots of suggestions that you get the book done first. You can't publish what you haven't written. I agree. Get it done, first. Don't spend five minutes worrying about getting published until you have a complete work that's been reviewed and fussed over.
Here are a few things I recommend for the writing stage. I’m mostly talking about trade fiction, but I think these apply fairly generally.
Writing app. Use a mainstream application like WORD. I use WORD on a Mac, but I’ve used it on PCs as well. There are things about it that I don't like, but when you search for an issue on WORD (even for Mac), you stand a good chance of finding an answer. Don’t go out and buy something, though. If you have Pages, use Pages. Later on you can decide if you want to move to a different application. For now, spend your effort on the writing.
Formatting. Don't do a lot of formatting. For a text-only book (a novel, say, as opposed to a picture book), I recommend extremely minimal formatting when writing the story. All I do is (a) set an indent for the first line of each paragraph for readability, and (b) use italics where needed. Nothing else. I don’t center things, or put chapter headers in boldface, or set different font sizes for different elements … nothing. Just type.
Outline. I always make an outline. It sometimes gets changed a lot as the book comes together, but I maintain an outline of the basic plot elements (at least, and sometimes specific other things like internal references). Especially with a full-length novel, it’s helpful to be able to review the overall flow without reading the whole book. If you plan to write a series, it’s exceptionally helpful to have outlines of each book. I refer to them constantly. An outline is also nice as a quick reference when considering changes, or reorganizing a storyline.
List of things to check. This could be style issues, or word use, or structural notes – anything that I want to remember to check. For example, when someone tells me, “you use the word muslin too often,” I laugh, and joke that I’ll change all instances of muslin to taffeta – and then I add the word muslin to my list of things to check. If it bugs one of your readers, it’s something to check. Similarly, when my editor returns a draft with several hundred proposed tweaks and corrections, I make note of the corrections that stand out as things I ought to check in the future. Otherwise I’m liable lapse into over-use of muslin in the next book, too.
Draft readers. Get some, and ask them to be blunt. Your best early draft reader is someone who won’t be hesitant to tell you what’s wrong with the story.
Pick at least a couple of people that you think are your target audience, as a baseline.
But also try to get at least a couple that seem out of your comfort zone, in the sense that you’re worried that they might find your story boring, offensive, dumb, a reflection of something wrong with you … people who aren’t going to gloss over things in your writing that bother them.
In the end, it’s your writing. You don’t have to change it. But I find it very helpful when someone tells me, “Oh, no. You’re not really going to make [this excellent character] say [this obnoxious thing], are you?” or “I’m rolling my eyes here, bud. This whole scene needs to go.” In the end, your readers aren’t going to be nice about things they don’t like. So find those things early.
Draft Reader escape clause. It’s a big ask. So give your readers an out.
I tell them this: Read a couple of chapters. If you like it, keep reading. If you don’t want to keep reading it, don’t. No obligation; no pressure. Either way, tell me what you think.
And I mean it. The last thing I want to do is to inflict my story on someone who hates it and just wants to get through it so they can tell me it’s great and get on to something else.