1. Do not refer to your manuscript as your "shitty first draft." Give it a nickname that suits your genre or your main character so you feel good about it... a 'scrappy rough draft' is a book that will fight to get finished but a 'shitty first draft' is one that asks to be flushed away.
2. When your negative inner critic tells you you're not a writer, thank it for its opinion, then ask it to leave you alone for an hour so you can work on becoming a better writer.
3. Find other writers to be in community with. This is critical. (I love www.creativeacademyforwriters.com - it's free to join).
4. If you want to succeed as a career author, treat your writing like a business with dedicated time every day to write, to do marketing, and to learn something new about the author biz.
5. Celebrate small wins. Writing a book takes a long time and you need to appreciate and acknowledge the milestones.