I have a really silly process.
1) If it's for a challenge, like for the portfolio, where you have to use x papers, x flowers, x ribbon, x staples, I go and find a kit that has everything I need first, and open ALL of the papers, ribbons, flowers, staples, etc that I really like. Then I kind of organize those the way I like them and choose photos to match.
2) If it's for a specific photo or photos, I go through and open EVERYTHING I like. Seriously. I find the kit and open papers, elements, and extras that I like... AFTER I open everything, I just sort of plop on papers and elements willy nilly. It is truly a process of "Oh. I like the texture of that paper. Let's throw that on as the background. Ooh, that flower looks nice. Let's pile on a bunch of these flowers here. Oh. Wait. Now there's not enough contrast between the background and the flowers, so let's top that paper with another paper..." So it's papers, elements, more papers. Or, sometimes I'll put the photo down and say "These elements really need to go here, here, and here," and I put the elements down, and then I think "Well, I used these elements, and this paper would look really cool with it, so I think I'll put this paper underneath there," and then I choose my papers based on my elements.
I guess I do a little of everything, because I just start with whatever feels... "right" at the time.