I show up to write fiction every day. That's the first habit to build. There's lots of writing online about getting to this point. I wonder: What's next? I write something every day — great. It's necessary. What's next? What's next if I want to get good, or if I want to publish my work some day some way?
An editing habit or practice of some kind has to come next, and that seems like a pain. First of all you've got to pick something to edit. General advice is to wait at least a week or two after finishing a draft before editing it, so that means if you're editing regularly you're going to be editing old stuff.
Editing means I've got to pick something. I've got something like ten complete stories eight of which are old enough to qualify. And I know that if I dug through my older daily writing documents, I could find probably a few dozen more drafts in various states of completion. There's a lot to pick from. For my sanity, I think I'll declare all drafts outside the ten recent ones "legally dead" until and unless I run out of recent work to edit. Otherwise there's too many half-complete stories to want to dig through.
On what basis to pick? Doesn't have to be the same basis every time. Picking is always annoying though. Maybe better to make a decision. "I will work on the newest/oldest thing that I haven't touched in the last three weeks." Something like that.
Also, at some point one has to find a place to put the thing. A submissions box, a web forum, a website, wherever. Could that be a habit, too?