To outline or not to outline? Some writers swear by their outlines. Others like their outlines loose, or prefer having none at all.
It all depends on you as the writer. What effect do you want the writing to have? Is it refined and exacting, or should it have an organic quality? Think about how the book may hold together for your reader and yourself. For me, I like having a chapter outline for nonfiction. This is a right-brained sort of outline that incorporates brainstorming so that I can have a view of all the topics I may want to cover. At the same time, I don't put these topics into a set order until the final writing, and I'm all right with making changes as I go.
For creative nonfiction, I use the facts of the actual story as my outline. I play with the form, and decide in the first or second draft if I want this to be in chronological, topical, or some other order.
For fiction, my characters lead the story. I'm apt to write character sketches, which are a kind of outline. Yet I put down the story in a state of surprise, not knowing what's going to happen next. I believe this sense of wonder shows in the final work. At the same time, subsequent drafts are where the form takes shape, where I connect all the threads and align the plot.
If you've never worked with an outline, try it! If you've never worked without one, try that. An outline can be fine tool, or it can be a crutch that keeps you from stretching your limbs. You decide what the work needs.