My books are fiction, and they are not set in the real world, although they are meant to seem as if they are, indeed, a part of the real world. They all have elements of the paranormal and magical in them, so instead of research, I have to rely very heavily on imagination. I do research fantasy creatures and myths, depending on the story I am writing. If I am writing a story with wiccans in it, I will research ingredients for spells and the different properties in those ingredients. If I am writing a story with a character who is a strict Catholic, I will research the religion in order to get my portrayal of the character right. If I am writing a story about vampires, I will research the folklore regarding vampires. But after the research is done, imagination takes over; otherwise my creatures would be just like everyone else's.
I do read a lot of novels in the genre I write. It helps to generate ideas. It helps me to see current trends in the genre. It helps me to see what works in the genre and what doesn't work. I don't think anyone should write in a genre that they rarely or never read. You have to have love for a subject to be able to write really passionately about it, and if your novel doesn't have passion, your readers won't feel moved by it.
In contrast, in the non-fiction book I am writing on health and weight loss, I am conducting a lot of research on the topic, along with interviewing others who, like me, have managed to lose a large amount of weight and keep it off. I am reading research papers and medical journals on the topic as well. If I want this book to be helpful and informative, then I need to make sure I know as much about the topic as I possibly can. I have lived a healthy lifestyle, lost over 145 lbs of excess fat and maintained the weight loss through a healthy diet and exercise regime, which accounts for part of my research - research through living it - but I owe it to my readers to keep them as informed as possible on not just my own knowledge of the subject, but on the current knowledge from the experts.