Bear Hug: A man once escaped a bear attack when he locked his arms and legs around the bear in a reverse bear hug, which made it confused and it ran off. If you're on your back and the bear is on you, it might be your last resort.
Calm The Charge: While it may be the last thing on your mind, calmly standing your ground when a bear is charging can be the best attack deflector. If you get a bluff attack as a warning, stand, wave your hands, and talk calmly to the bear.
Go Sideways: Because of the bear's huge upper body and neck muscles, rotating their heads side-to-side is difficult. Keep moving to the side to make it harder for them to see you... or see your attack on them.
Play Dead: Okay, this doesn't work when a bear has stalked and attacked you, but will work with bears protecting their cubs or territory. So if you are a lover, not a fighter, play dead.
Eye Gouge: Big bear has you down and is seconds away from having you for dinner. If you have a free hand left, drive a finger into the eye. Blindness ends all excursions.
Pepper Spray: Mace, pepper spray, wildlife repellent... they are all great at making a bear retreat. If you don't have any with you, read the other steps listed here.
No Hiding: This seems counterintuitive to staying alive, but hiding will also wake the killer instinct in a bear. Especially stay out of tents or trees. That's practically daring them to come after you.
Walk: Running from a predatory animal can trigger the hunter, so walk away with purpose. But if you must run, head downhill. Bears kind of suck at going down, but are awesome running uphill. And their endurance is awful, so keep going.