In time, your rabbit will let you know when he wants head petting. He will start approaching you, placing his paws in front of him and lowering his head. Contrary to what you may have seen in movies, rabbits are not apologizing or expressing guilt when they display this behavior.

Rabbits with partners (rabbits they have bonded with) assume this same position when they want to be groomed.
Once your rabbit begins approaching you for head petting, you can be sure that trust is being established and a good bond is being created between you and your bunny. Always pet gently. Rabbits have very delicate skin and are fragile in many ways.
Petting your rabbit’s tail or bottom area is different. It mimics what a predator would do in the wild. If a rabbit detects a predator, he will use quick evasion techniques to get away. For that reason, predators surprise rabbits by sneaking up and catching them from behind. Even though your pet rabbit is bred for domestic purposes, his natural instincts are still intact.
Avoid petting his hind area until he trusts you. Sometimes, even a good bond between you and your rabbit is not enough for him to let his guard down. Your rabbit should be able to overcome the lack of trust that exists when you touch his hind end area, but it may take time and patience. Whatever the case with your pet, respect his preference and remain gentle. Since rabbits are prey animals, their instinct to protect themselves in various ways is part of their base nature.
Bonding your rabbit with another rabbit or pet is an entirely different topic which is not addressed here. For more information on Rabbit Care Basics, click here for the free course.