Some things, especially ones I've done many times, I'll not plan at all. Sometimes things I've never done I'll do off the cuff as a sort of initial experiment. Large and complex projects, I'll plan out the design in detail, but I don't always hold myself to it. I almost completely redesigned the frame and elements of one complex project while I was making it, as I thought of a better solution which hadn't occurred to me until I started. I guess the whole thing is very fluid.
In terms of proccess, I have a standard way I lay things out, especially for very structured and repetitive tasks like making nails or arrowheads, or raising where I need maximum effeciency each heat. I've worked out these 'plans' in the course of doing them, and once I hit on something that works very well I rarely deviate from it, unless for special circumstances or another idea.
Cheers,
Nick