What is the smallest step you can take? 
Charles Roper wrote a great piece called Kaizen in which he talks about breaking down big things into small steps:
In taking tiny steps, we become accustomed to the change. We get used to it little by little. As time goes on, we increase our exposure to the change. Habits form, routines solidify, and, as if by magic, we find we’ve grown. We’ve made progress. This is how we defeat the fear. We practice. We do something so easy it seems stupid. That’s the trick.
Charles asks what is the smallest thing I can do? in the context of writing daily:
Five minutes of writing per day, perhaps? That sounds reasonable. How about one sentence? That’s pretty Kaizen. Or a tweet’s worth? Ideal. So I’ll aim to write just a tweet’s worth of something every day for 30 days. A paragraph, maybe. Or just a sentence or two. It’ll take around five minutes at most.
That’s a great approach to daily writing. But it applies to much more than just writing. If there’s a habit you want to build, ask what is the smallest step you can take?