Bonding, and establishing trust between you and a bun can often take some time, and patience, which can feel a little unrewarding at times, but when it happens, it is so worth it.
Try, like Laura said, to get down to his level (even lying on the floor) as much as you can when you are establishing your relationship, because he is much less likely to feel threatened by you, and much more likely to approach you, be inquisitive etc. Bunnies are naturally curious by nature, so if you sit down, read a book, and sort of 'ignore' him (obviously you will be aware of him and supervising), he will be much more likely to come to you and demand a stroke.
Awww that sounds so lovely. Gentle grinding of the teeth is like a cat purring- real contentment.
After you have 'groomed' him for a while, try placing your hand underneath his mouth, for a groom in return (bunny kisses are so adorable- my buns love to lick me. I can't tell you how many times I've been sat barefoot at the computer chair- shocking seeing as I'm on RO 24/7
- and felt the bunny kisses on my feet lol).
Jen