Hello hautecouture_02
We have a couple of threads on fashion illustration in general
There is some good advice in the aspiring designers' thread too
Here are a few sort of related threads in the Careers & Education and Art & Design forums:
Aspiring Designers Lookbook - share your work
tFS Fashion Design Sketches Central
The Design Portfolios Mega Thread
How to draw...
Designer Sketches
Sketchy Behavior- Fashion Illustrators
I myself haven't used books
I learned to just draw and simulate textures w/ paint and other mediums
and also draw the human form well
Some people suggest a format for creating model's bodies for fashion illustration
As for designing fashion, I think it's helpful to learn about actual construction
For example if you design something, how do you know if you can actually make it.. if it's possible to realize, etc. ...