Have you ever had trouble figuring out the plot of a sequel that is as interesting as the first book? Any advice on getting past this?
No problems as yet. I keep two things in mind, here:
1) I try to plan out a loose sense of what the next couple books will look like before I even write the first one. I like the sense of an overall arc and for things to go in a direction that is (or at least seems!) roughly planned from the get-go.
2) I don't put everything I have into the first book. Some things -- secrets, conflicts, escalatory moments -- gotta wait for follow-up books.