Try timing your writing sessions

Something I’ve learned here, other than we’re all doomed, is to take an kitchen timer and set it for how ever long you can conceive of writing something. Since I’m working on four different things write now, I set it for 1/2 hour. It’s amazing how that countdown spurs me.  
When it dings, I wrap up what I’m doing. I make a backward outline, meaning I write down what’s happened in the story not what’s about to happen, write one line to spur me the next time I write, reset the time and start on the next thing. 

I also time breaks. I give myself ten minutes or fifteen minutes to do what ever I’m going to do. Then I get back to it.
It works for me.   Peter Schuyler,  Screenwriter in LA.