Wow. It was inevitable this would come up sometime. There's no thread in the knowledge section for this one, but there is for the next problem you'll encounter -- aiming the lights. Gordon Nichols wrote that one, so it's an easy-to-follow remedy.
As for the clips, they only work one way. Theyhave to be one or the other side up, legs outward toward the bezel and the elbow toward the light, and the first pair have to be put in at almost opposite sides pretty much at the same time.
If I remember correctly from when I dealt with that giant pain in the butt, the clips should go in with an evenly distributed pattern, the more the merrier. You'll want at least six clips in each bucket.
Someone here has the right answer, but you'll know you have it right when there's tension on the clip. They only work in one orientation -- so you've only got to eliminate three incorrect ones to get it right!
Good luck! I'd perform the operation over a dark-colored blanket, since they'll pop out and go flying at the first opportunity. You might also want to make sure the pattern in the glass of the headlight lens is oriented how you want it if a "crooked" headlight would bug you when you're finished.
Not the kind of job you'd want to repeat if you could avoid it.