I have a few fashion illustration books and quite the enthusiast myself. I'm not sure where you stand in illustrations-- are you just getting started? honing your skills?
I really like
Fashion Sketchbook by Bina Abling. It's actually a textbook for school, but it's really great. It has a wealth of knowledge hitting different areas such as drawing the croquis, menswear, childrenswear, specifics of accessories, rendering fabrics etc. Some things are step by step, other sections give you visuals as examples (which I think is great, it gives you more freedom). I think this book adheres more to industry standards of how to draw clothes and models.
Fashion Illustration by Bethan Morris is great for really the
illustration aspect. It's more artsy, so to speak. It shows you how to keep a useful sketchbook, artistic techniques using different mediums, etc. Kinda hits different sections briefly. For a taste of inspiration, there's a section on different illustrators with some of their pieces and an interview portion.
I'm hoping to buy
Contemporary Fashion Illustration Technique by Naoki Watanabe. I was reading some of it at the book store the other day, and I think it's also great. If you have a good grasp of croquis (or if you don't, has a section on it too) this book really goes into detail about how to render fabrics using different mediums, and other specifics. I like how thorough it is.
If you have any more questions, feel free to ask, I'll do my best to help