Writing must be a lot like mountain climbing. The task initially seems insurmountable, arduous and mind boggeling. To overcome this I am sure that a mountain climber plans the route, gathers the gear, anad physically and mentally prepares himself or herself for the ascent. It is exactly the same with writing the novel.
The best planning advice I received was “create a premise, a ‘what if’ and expand from there. What if Hitler had won the war. What if the first moon landers couldn’t leave the moon. What if Hinkley was a better shot. The possibilities go on and on, and once you have settled on your what if, expand it.