If you want to be a novelist ...
learn to write short stories
Every year I have at least one student arrive for class who 'doesn't want to bother' with short stories because they're working on a novel.
Yes, there are writers who manage to get a book published without working through the apprentice stages of short fiction, but believe me, they are rare. And yes, I don't have a published novel myself yet ... but I have had something over 120 stories published in three years, over half of those in paying markets. I believe it's only a matter of time before I crack the novel business too, and I base that belief on some hard evidence:
1 - I know I can write fiction because people pay me to do it.
2 - I know I have a market for a novel because people read my short fiction.
3 - I know I can work with an editor on a novel because I've worked with dozens of editors on short fiction and spend a fair proportion of my time editing the work of others.
4 - I know that when an agent or publisher looks at my biography they will feel confident I'm not going to be a one book wonder, because I've written so much, and so much of it to order, that we can all be confident I'll keep writing marketable stuff once my first book is on the shelves.
All those writers who slave away on a novel without proving any of these facts will probably come up against one unpalatable truth. There are thousands of good writers out there trying to place their novels. The book business is a money business, not a talent business. Given a choice between a good writer who has no experience and a good writer who can be trusted to behave sensibly over edits, to keep turning out work for years, and already has a platform of readers who will probably buy that first book - which one do you think the publisher will choose?
And that's why I urge my students to learn to write short stories.