Hmmm - I'm not sure I have a set one. I tend to scrap according to my mood and what I'm currently working on.
Sometimes its product driven because I'm using a scrap kit or have something specific I just want to get onto a layout so I build my entire look around that product or those papers. I find pictures that match the paper or embellishments and then work a sketch in my mind that co-ordinates with both.
Other times I have photos first and find paper and embellishments to work with them.
A lot of the time I have a sketch in mind and then find pictures and papers etc that go with the sketch.