Try to find his/her favorite spot to be groomed/scratched. For example, my horse loves it when I itch her mane. If you find a sweet spot, stick with that spot for a while to make them enjoy standing and being pampered
I would try maybe first starting with your hands and petting him as you would grooming. Then go from that to a soft brush and then advance from there. Get him used to that contact and ease him in to get him to relax.
What worked for me was just grooming them every day to get them used to it. Also rewards help a lot. Just curry or brush them and if they don't nip or move, give them a little animal cracker or somethin