Fabric manipulation...

The manipulation of lengths of fabric, either man-made or commercially produced, can produce very valuable results. Raised sections and gathered, twisted or folded areas can highlight shadows and textures as well as shapes and lines. I have found the following book to be very useful:
Colette Wolff, The art of manipulating fabric Iola, Wisconsin: Krause, 1996.

Crochet and flexible fibre design...

I find that some specialist books on specific fibre techniques can provide pathways to new ways of thinking about fibreart compositions, as well as design problems and solutions. Crochet can be a very useful fibre technique because sections of a fibrework can be started and finished in a very spontaneous and flexible manner. Different sections of crochet can also be joined together, or combined with elements created through the use of other fibre techniques such as knitting, weaving, basketry or sewing. Here is an early text that advocated the development of “free” forms of crochet:

Del Pitt Feldman, Crochet discovery and design New York: Doubleday & Company, 1972.