Writing a novel is a marathon. And before you run a marathon, you have to train. You run every day, you eat healthy food, you drink lots of water. You slowly build up your endurance over a long period of time until you're finally ready, and then you run a few practice 26Ks in training before Marathon Day.
You lay the groundwork for a successful marathon.
Writing a book is the same thing. You do character analyses; you do outlines; you plot out your novel on index cards and whiteboards. You write a draft, then revise it, then revise it again.
And just like running a marathon, you could try just running one as soon as you buy your first pair of running shoes, but it's much better and easier, and you have a better chance of finishing, if you lay down some of the groundwork first.
What groundwork do you do before drafting your novels?