Ever since I got over (most of) my fears about my serger, I've been picking up books about it, too. Most of them are interesting, but they often don't go beyond the very basics and if you have to troubleshoot, you are on your own.
Sewing Essentials: Serger Techniques covers the basics, but also goes well beyond them. In particular, one of the challenges I have with my Singer 14T967DC (it's discontinued, but if you have one, the workbook for it from Singer is pretty great), is that, since the tension for the loopers/needles are set automatically, I don't always have a good sense of how to change the setup. I mean, I can balance a stitch, but I have not been able to get the rolled hem to, well, roll.
Until I had this book! It covers not just how to set things up, but what to do if they go wrong. And, by the way, it's not just you, you shouldn't TRY to turn corners while using a rolled hem. Just end it, use a little fray check, and go on with your life. (Yay!)
You may know the author, Pamela Leggett, from Pamela's Patterns. I haven't used any of her patterns, but I love her writing style and I have closely read all of the pieces I've seen from her in Threads magazine.