For me, I've always had the issue of not being able to write large amounts for something. It may be my engineering way of thinking, but when someone writes 2 paragraphs, I can usually explain the same thing in 2 sentences, without really losing anything. Writing concisely is useful, but isn't always good when you want to make a narrative.
One way I've gotten better at writing more is by making characters for stories. Having bio pages (especially for anime-style characters) lets me write about specific traits/abilities/etc. The crazier an ability is, the more I would need to say in order to explain it properly.
I guess this would also fall under writing more often. (More character bios means more practice to write something).