My horse had never been groomed before in his entire life before I got him, and he was 18 years old! So I had lots of trouble with him. He liked to swing his head around and try and nip me, so eventually I got so I just carried on grooming, just watching him out of the corner of my eye, and let my elbow meet his mouth whenever he swung around... I only had to do that about twice, then he chewed and understood, and he has never done it again. Then he seemed to enjoyed walking backwards, just step by step till I got so frustrated. It didn't matter what I did, he just liked walking backwards.
He also yawned and did a whole lot of stuff, but just trying to be as naughty as possible.
Not funny then though. Anyway, he now is the best horse to groom, and I don't need to put a halter on him even, he just stands there quietly. He seems to have got used to it, and now, for once, seems to enjoy it!
I'm sure your horse will sometime begin to like it! Oh, one more thing... I groom my horse MUCH softer than any other horse, he's very thin-skinned and I don't make circular motions with the rubber curry comb, I just do it straight. After I changed those two things, my horse loved it! Maybe you should try swopping things around and seeing if there's something that your horse would prefer.