What I don't recommend is beginning at the beginning. Since you need an ending to work toward, begin with that ending.
continuing a project
#84: Staying Focused Long Enough to Write a Novel
Until you make your abstract goal more solid and figure out what makes it personally meaningful to you, it will keep losing out to shiny new ideas.
#67: New Ideas Stop Me from Finishing Anything
Today is the fifth Tuesday of the month, which means that my answer to this heartfelt letter is available exclusively to my Patreon patrons.
#21: Stopping and Starting
Nothing gets in your way more than a creative writing degree and a lot of practice doing other kinds of writing, both of which fill your head with all sorts of ideas about what writing should be like.
#9: You Are Your Own Muse
Inspiration is intermittent and fleeting, and writing without it feels unsatisfying or clumsy by comparison. So we chase after it and try to get inspired again, or we give up on the old project and start a new project, as though that were the only way to write well, or to enjoy writing. It's not.
Story Hospital 