There are so many variables to weigh and balance when starting a novel, it is silly not to spend considerable time mulling things over, working out the conflict, major scenes, character background and personality, setting, deciding on a point of view, and a thousand other things before you actually begin writing the book.
Some people dive right in and just start writing, claiming that they don’t know what will happen or even “who did it” in a murder mystery until the characters reveal it to them . . . though I suspect these claims are false and yield shoddy stories. Still, maybe that approach will work for you, but most of us need to plan well in advance.
For the ending to satisfy, you should consider it when you write the first page. I can’t imagine any novelist is like Mozart, seeing the entire story before him all at once in one fantastic flash of inspiration. Therefore, if you just start writing before you have a good idea of where you’re going and how you’ll get there, you will likely end up getting lost. At the very least, your opening will not be as effective as it would otherwise be if you could lay some subtle groundwork. If you don’t plan ahead, you’ll probably write some okay stuff, get stuck, not know where to go, realize you should have done something else 40 pages ago, scrap the last 40 pages, etc.
I wrote “essays” on each of my main characters. I pretended that my novel was already written and a professor told me to write a character analysis of each major character in the book. Basically, I looked at their personalities and histories, then plotted their character arcs—figuring out how they would change during the story, which scenes would catapult that change, how the background info was relevant (or not) and how to reveal it during the story, etc. This was a huge help!
I also wrote brief paragraphs about what I consider my main themes: explaining each theme, how it is introduced, developed, and what the story says about it in the end. If I found that a theme got “dropped” somewhere, I had to make decisions: do I scrap that element of the story? Do I find a way to “bring it back in” by the end? What changes would need to be made? How would this decision affect other factors in the story?
Use the computer, note cards, post-its, or whatever you want—but get organized before you actual begin writing that novel.
Keep in mind that IT IS OKAY TO DEVIATE from your outline. And you will. When you do (usually because your characters demand it), you may be able to easily steer the book back on course. If you can’t or the characters won’t let you, you’ll need to start outlining again from that chapter onward. Or I suppose you could go back and revise the character so that he/she would make a different series of decisions that would allow the book to remain pretty much on track with your original outline—but even that involves going back and doing a lot of rewriting and seems odd.
NOTE: It is true that you can discover a lot by writing, but if you do so without an outline or map, the writing will be without direction. As a result, you’ll end up cutting much of it. You might surprise yourself and come up with some fascinating characters, scenes, and plot points, but most likely, you will have to rewrite much of your work, so outlining can save you a lot of time. Diving in and writing while brainstorming might give you a rough draft. More likely, it can be a useful way to get to know your characters, but you’ll still have to do major revisions—possibly even starting over once you do know where you want the story to go. I know several authors journal as a character. They are often surprised by what the character will reveal to them during this process and some of that information makes it into the book. But that’s a journal. It isn’t the novel. That’s the author “doing research” to get to know the character and those journal pages will not be in the novel itself, so journaling is not writing the novel.