I personally found setting a count goal, or chapter goals (e.g: 2-3 chapters of this story per day, etc.) helpful. Over time this was accompanied with spreadsheets that calculate how much was done per day, per week, month, year etc. and now I don't need goals that much anymore because it's reached a point where it feels strange when I skip a day of writing. (Though don't get me wrong, I still organize what I'm going to work on and how much time I'll spend on each series.)
There are some good already-made spreadsheets out there, and sites to calculate how much you need to get done a day (they make plans for you, it's great) when/if you're short on time. If you feel like those could be of help to you too, I can go fetch the links real quick.
If you do set up count goals though, I recommend going from 500 words (or whichever your average count is), then adding 100 words per day, until you reach a number you're happy with. It's usually more of a matter of getting that habit in your life, at least from what I've seen/experienced. There are other things that you can do, but I've found this stuff to be the most helpful. Good luck with your writing journey in either case, hope you figure stuff out!