Start with an outline, listing and describing the major points of the plot and characters. Write it in the notebook. Set no more than seven days to accomplish this.
Next, take a lateral approach. Stealing a page from cinema, so to speak, sketch storyboards in the sketchbook, basing them on your outline and illustrating its major points. Skill is not a prerequisite; stick figures will do. In this way, visualizing the complex interplay of plot, character and setting becomes easier. Again, try to accomplish this quickly, in perhaps a fortnight, at the most.
Begin writing the first draft of your novel in your notebook, computer or wherever you feel comfortable writing it, but keep it orderly, keep it short and most of all, keep it action- and dialogue-oriented. Depending on the time you have available, this process needs at least a fortnight to complete, but may take six months.
Chances are that in the midst of outlining, sketching and writing the solid prose, some extra writing took place. Good. Never fight the impulse to jot something down. Look at this material; find uses for it within the overall draft. If, however, it takes more than an hour to find a place for scrap material, move on; it doesn't belong.
Polish the first draft, removing excess scenes that do not support plot, setting or character development. In this first revision, concentrate on the obvious points of awkwardness, such as bloated asides, stilted dialogue, ambiguous details and other elements that steal from rather than add to the novel's storytelling, editing out as much as possible. In gutting the novel, you gain freer rein to add crucial elements that were crushed for space before.
On commencing the final draft, devote attention to the finer points of prose and the artfulness of the wordplay. Work over each scene laboriously, until it becomes a simple matter of whether a comma ought to be removed or kept.