I call it "The Space Model." And I drew a handy dandy illustration in Paint to help you visualize it! Below is my paraphrase of his advice, but of course, it was better coming from the horse's, er, the fellow's mouth.
Non-Negotiable Core: Here you put your few non-negotiables, the essentials that a prospect bf/gf/spouse must have. For example, "must be a Christian and have a personal relationship with the Lord." No arguments, no bending, isn't relative to how wonderful the guy is. If he doesn't have the core qualifications, he's not even on the wish list. Limit what you put here or else you really are picky (those are my words, not his).
Ring of Fire: Here you put the qualities that are almost important enough to be core essentials, but, depending on the person, could be overlooked, maybe. In the words of my friend, if you and the other person are able to put out the fire, then you deserve marriage. But if you play around with these, you'll get burnt. Some people might put "Calvinist" or "Non-Calvinist" here.
Asteroids, or Bricks: These are all the other details. Some are big and important and almost go in the Ring of Fire. Some are preferences, like "he needs to be taller than me." (Hopefully we can be sensible and put that in our Asteroid Belt and not in our Ring of Fire? Maybe we can make it one of the big asteroids near the Ring of Fire??) Like bricks, you get enough of these objections in a relationship compiled one on top of the other and suddenly you have a wall. Can the wall be torn down if the two of you work together? If so, great! But maybe the wall has been reinforced with metal girdings and glued together and ain't budgin'. How you handle the asteroids or bricks is up to you. These are topics to navigate one by one with the guy in your life.
My checklist tends to be a more nebulous this, this, this, this, that, not that, not THAT, maybe this, wish this, hope there's this, etc. I think the Space Model way of prioritizing what you want in a potential spouse is a good way of gaining perspective about what really is important to you and God's will for you.
So when Well-Meaning-Relative wants to know why you aren't interested in Such-A-Good-Guy, rather than wrinkling your nose in that all-encompassing facial expression that says, "Uh uh, please don't bring up such a nasty suggestion again," you can say, "Ah, well, you see, our differences land us in the Ring of Fire and I'm not willing to go fight fires over him," or, possibly, "Hm, you're right. We only have a few asteroids between us. Maybe I should give him a chance!"
In the meantime, go read this post by Holly Stallcup that sounds eerily reminiscent of my own thoughts!