One from 2009 talks about keeping your characters true to themselves and developing a great supporting cast. You can read it here.
That same author, Carrie Vaughn, has another post about writing series. One section that really resonated with me was: “I want to share something participating author Paul Witcover said during this discussion: Even first novels, or stand alone novels, have a backstory. It’s just that we don’t worry about including it all. I think this is incredibly important to remember: When you’re writing subsequent books in a series, you don’t have to tell a new reader everything that came before. You only need to tell them what they need to know to understand what’s happening right now, and you can do it in a sentence or two.”
You can read the rest of her insights here.