500 words per day is plenty. John Grisham began his writing career as a lawyer. He got up early every morning and wrote one page. You can do the same.
Have an outline
Write up a table of contents to guide you. Then break up each chapter into a few sections. Think of your book in terms of beginning, middle and end. Anything more complicated will get you lost. If you need help, read Do the Work by Steven Pressfield.
Have a set time to work on your book every day
If you want to take a day or two off per week, schedule that as time off. Don’t just let the deadline pass. And don’t let yourself off the hook.
Choose a unique place to write
This needs to be different from where you do other activities. The idea is to make this a special space so that when you enter it, you’re ready to work on your project.
You Have a Deadline…
It can be a word count, percentage of progress, whatever you’d like. Just have something to aim for, and someone who will hold you accountable.