The basic formula is stick to about 3 main colours when choosing fabrics. (don't try to match shades) and use a variety of scale fabrics.
I added a couple of vintage fabrics to this quilt.
I decide the colours to put together as I go, using a design wall or laying out on the floor.
It was then sent to the machine quilter and crosshatch quilted, then bound.
My very favourite poster by the talented Shannon Lamden from Auntie Cookie. (sorry I don't know how to link yet so do a google)
::update:: here is a link to Aunty Cookie!