The advice would be the same for any kind of fiction. Keep writing, and keep sending things out, not to friends and relatives, but to people who have the power to buy. A lot of additional, useful tips could be added, but this is fundamental.
Fred SaberhagenThe Swords were still interesting but by then a cast of characters had started to appear and go on from book to book, and other things about the world began to feel constricting. And there were other things I wanted to do, so I closed the series up and stopped it.
Fred Saberhagen