Research is something that, with most books, you will have no choice but to do at some point during your writing. If you are writing a fiction novel, than you will need to research a variety of things for your book?
Some things you might need to research when writing a fiction novel:
Where are you setting your story? How is the setting important to the story and the events within the story? Have you done enough research on your setting to be able to write about it? Is your story going to be in a different world? If so, what do you need to research in order to accurately portray this mythical world?
Some authors who have book set in the present day world use needing to research their chosen location for their setting as an excuse to travel. some authors keep their stories located somewhere that they already know very well, but even then, there is research that might need to be done about the location. If the setting is local but in the past, local museums can be a great help in your research.
If your protagonist or antagonist are using weaponry of any kind, you will need to research the type of weapon and how it is used. for example, different guns have different weights and caliber of bullets. Some guns and rifles take longer to reload than others ans some guns and rifles shoot faster than others. some shoot more bullets before needing to be reloaded than others do. You have automatic weapons and semi-automatic weapons. Which will your character be using? And, taking a moment to look back at setting, which weapons are legal or illegal to carry in your story's location?
Archery has the same differences to research. there are long bows and short bows as well as cross bows and compound bows. Do you know what makes each of them different? And what about the way they feel to be used? Does one take more strength to pull back than another does? How fast can each type shoot arrows? What types of arrows do they use? Did you know that the compound bow was created in such a way that it reduces the holding weight when they reach full draw position? Or that the recurve bow is the only bow style allowed at the Olympics?
there are many other weapons that your characters might make use of, such as swords, throwing knives, poison darts and many, many more. An extra step for your research would be to take a class that teaches you how to use the weapon. Once class might be enough to give you an idea of the level of skill and difficulty and how each movement feels for the person wielding the weapon.
There are many types of research needed when writing a fiction novel, more than I have mentioned above, but what about when you are writing a non-fiction novel?
Some things you might need to research when writing a non-fiction novel:
The research needed when writing a non-fiction novel will vary according to the topic you are writing about.
If you are writing a biography, you need to research the person you are writing about and the time period during which they lived. you might need to research the people who were around them.
If you are writing a how-to, then you will need to research the type of thing you are writing about more specifically. For example, if you are writing a book on how to raise children, then you would need to research the current theories on child-rearing. If you are writing a book on how to do your own accounting, then you need to research accounting methods. If you are writing a book on how to start a fundraiser, then you might want to talk to people who run charities and ask how they run their fundraisers. You will need to tailor your research to your topic.
If you are writing a guide, you will still need to tailor your research to your topic. For example, you will need to research locations, hotels, car rentals, restaurants and more if you are writing a travel guide, but if you are writing a guide to haunted buildings, then you will be researching the history of those buildings as well as interviewing people who claim to have had ghostly experiences in those buildings.
Non-fiction books can be written to teach how to do something, to document something, to express an opinion on something, as a memoir, as a scientific research topic; they can be biographies or autobiographies or even diaries; they can be photo books and user manuals. There is a huge variety of non-fiction books that can be written, but none of them can be written without some level of research beforehand.