1. They tend to write many books in a series.
2. Specific genres, like horror, YA, erotic and thrillers seem to do especially well.
3. They are incredibly self-disciplined and productive if Sean, Johnny and Dave are anything to go by.
4. They become experts in online marketing.
5. Some extraordinarily kind sharing of qualities like technical expertise goes on in this space. Here’s the article on self-publishers earnings, which is testimony to this.