The question is normally asked in the field as “Are you a plotter or a pantser?” (Pantser is shorthand for flying by the seat of your pants, with no plot.) My answer is normally “yes.”
I started out writing detailed plots and some books still require me to — for instance, Noah’s Boy, the last one I delivered to my publisher — yet some books refuse to be plotted. Sometimes I can only see a chapter ahead.
However, for beginning writers — i.e., anyone who’s written fewer than five novels — I advise plotting the book in advance. You see, I think the reason I no longer plot that much in advance is that I’ve internalized a lot of the rules and sense of what a novel is. I should have, after 23 novels.
This said, writing a novel is an intensely personal endeavor. I’m going to give several methods which will work, from full outline to “high points” outline, to a couple of paragraphs pinning down your idea. You can pick whichever you want to use, or none — we’ll still be talking about how long it will take to write, etc., even if you’re flying by the seat of your pants. Be aware that pantsers who are inexperienced at writing usually end up having to do heavy revision at the end. This doesn’t mean it’s bad, just something you should know.