Early in a book project, research is a major part of the work. No matter what kind of book you’re writing, you’ll need to do some research, if only to find out (for instance) which way the one-way streets went in a given city in 1965 (or something similar.) Because among the community of readers, there’s always the expert who knows, and will be glad to tell the world, if you made a mistake. If your own desire to write perfect books ever flags, you know there’s this person, ready to purse their lips and write a scathing comment about your carelessness where it will do you the most harm. (Nicer people pursing their lips just write you, which still stings but at least allows you your dignity.)
Making up your own worlds doesn’t get you off the hook, either. Did you put a granite mountain where it could not (geologically) be? Someone will complain. Does your imaginary society not fit the “rules” someone has set down for its economy/politics/military? Someone will complain. And besides, if you are making up your own world, you do so because you want to show you can do a good job. Hence…research.
So the early part of a book involves both the research you knew you’d need, and the research you find out about early. I enjoy research and sometimes have to employ extreme measures to make myself quit with the research and write the book. (But then, I also enjoy writing, so that doesn’t happen too often…usually only when a new research topic has opened the door to a vast new territory and I’m in explorer mode.) Research encompasses fields of knowledge, specifics of history, and all the way down the scale to vocabulary (what do you call the part of a cart to which the horse’s harness attaches? What is a reasonable name for a new protein found in an SF-mystery-thriller? What are the rules for naming new plants on this planet?)
Research often runs alongside the writing…you get to a point where you realize “I don’t know how that would work,” and you have to stop and find out. There’s a village mill…water-powered…OK, is it an undershot or overshot water wheel and what effect does that have on the efficiency of the mill? How are different “grades” of meal/flour produced? What kinds of accidents (and what kinds of injuries) could result from working in the mill or playing around the sluice?
Research with fights (of any type) may require staging such a fight; if you want to write stuff with sword-fights in it, go find a group that does sword-fighting for fun or profit (profit would be theatrical fencing, primarily), do enough research to know how accurate the group is (some are just flailing around.) I’m fortunate in having a group who will help me work out fencing problems, including multiple-person fights, when I need them. Military history is a fine source of realistic engagements (they all happened) with a variety of weaponry. But personal experience, if broad enough, is a huge contribution. One day hike teaches more than reading three books on hiking, and a few seasons of hiking in all weathers and all sorts of terrain teaches a lot more. Every new skill–even though the rriter won’t be expert in it–teaches what mere words can’t. (Hence my much better understanding of scything after scything only about a half-acre.)
Later in the book, during revision, you may find that you still have research needs. Alpha readers are one form of research (the question being, does the book work?) But their comments may suggest other topics the writer needs to check on–or re-check. So may re-reading by the writer. This can be annoying (not the comments–the need–when you want to hurry through revision–to go back and check on something you were sure you had right, that now just doesn’t feel right. Would that land, as described, really support that many [pick your livestock]? Could that crop be grown there? Could a force armed with [pick your weapons] really stop a force twice its size armed with [other weapons]? Under what conditions? Under what conditions would a character previously shown to be [name your qualities] act in a way that seems impossible with those qualities? And another form of research is a reconsideration of alternative lines the book might take–and which might be more satisfying. Which makes more sense, that X hurtles off in a snit, or stays to argue and then reconcile? What would make each alternative make sense? Which alternative opens up satisfying and productive plot lines for the future, that have a hope of ending up where they should, in that very complicated but fulfilling Turkish-knot embellishment at the end?
If you think this means I’ve been digging into the research again, you’re right. Examining every motive, every action (including the motives and actions of those who aren’t even onstage), checking facts against reality and against previous events/characters/etc. in the book itself. Though I have never yet reached perfection, it’s important to do this–important not to skimp this late phase of research–because the closer to perfection it comes, the more you, the readers, will enjoy it. (And I’m telling you this out of intense self-protection at the moment, wanting you to know that if you find a nit to pick later, I tried really, really hard…)