Yeah, you will need to make an outline listing the main sequence events of the story. Each of those main events could become a chapter. After those events are defined, your next step in the outline would be to describe sub-events to each of those main event. If you plan on having branching story lines (for future stories), this is where you will want to implement it. After you have clearly defined the main sequence of events, you could probably begin writing pretty easily. You will essentially be filling in the blanks between each event. The amount of detail you include will determine the overall length of the novel.
You will probably also want to develop a lengthy and detailed biography for each character in the story. You will want to be able to maintain consistency throughout the book while also being able to clearly define the characters to the readers. The biographies won't necessarily be included in the book, they will just serve as a guide for you to adhere to as you write. You could also apply the same process to the setting or settings of the story.
This is how I would do it at least.