Hemingway did this shit, so listen up.
Writing in a lot of ways is like exercise or gardening. Even if you enjoy it as a hobby, it's hard get in that harness and start pulling.
Sometimes I'm staring at a whole blank page, and other times it's the white space near the bottom. For me, it's been easier to pick up where I left off than start from scratch. So what I do is try to leave a sentence half finished so when I get back, there's a jumping off point.
It's tough to do at first. I'm always afraid that I forget where I was going.
The preeminently talented Robert McCammon had this tip. "Someone asked me if I ever get “stuck”. No, I don’t. Here’s my secret: when I finish writing for the day, before I get up from my desk I always type one letter for the next line. The letter is random. D…H…K…B…whatever. So when I come back to work, I begin the next sentence with that letter. Might not work for everyone, but it does work for me." Side Note: If you haven't read Boy's Life, do yourself a favor as a writer and get it now.
So I've done a couple of different things. From dashing off a rough "Where I was going" note to having a "If it's cool enough, I'll remember it tomorrow" attitude.
Sometimes, I just finish off the damn sentence anyway.
The key is that I don't spend another 15 minutes thinking about it. I just go with my gut and close the file out.
For my workshop, I even do this with half a chapter. (So as not to drive my workshop mates crazy, I submit at least a full chapter. So this means I am always half a chapter ahead.) The five days that I'm critiquing my fellow writers' work, my hind brain is working out the rest of the chapter. This has been actually more helpful than the half sentence technique.
Yeah, detailed outlines are not my thing.