I rarely use patterns or books. I design whatever it is that I need. I mostly do practical things to wear like mittens, hats, and scarves. If you know your gauge and have a measuring tape, you can make almost anything. One book is great for designers. It has "how to" instructions for a variety of projects like mittens, gloves, vests, etc. using various gauges and yarns. I would call it a master pattern book.
Teach Yourself Visually-Knitting Design.