I am a project vs stash shopper. I will normally pick my focus fabric first and then pull from that what other colors/fabrics I want. I usually have a photo of the project with me. Once I've gathered what I think I want, I try to lay them out with the appropriate percentage of the bolt peeking out from the others in the order of most to least.
Can be a tedious process but it's what works for me. Sometimes the focus fabric changes either along the way or even at the end. BUT by then I've at least gotten the bulk of the fabrics I want for that project. Might have to shift which one is getting used for what part of the project or trade something out but the bulk of it is there.