Escaping the back. The first thing you're going to do is make sure you protect your neck. I keep my chin tucked in, and I have my hands up. I'm holding down this hand so that he doesn't work his hand into my collar, like so. I keep this hand protected, and I keep this like so. I'm going to bridge and get my head to the other side of his body.
Should I go to this side, my opponent gets to choke immediately. So you always go to the side of the arm under your armpit. Here, chin tucked as much as possible. I get to this side here. I've got some weight on my opponent. He can't move so freely, although I'm the one still in trouble.
The hook. I take my hand, get to the hook, get it off, and quickly put my hips over it. As I take my hips out, I look at my opponent. If I get here, and I start turning to run, he's still on my back. Never do that. Common mistake. Big mistake. People make this mistake all of the time.
As soon as I get my hips over his leg, I look in his direction and keep hip escaping. If he's smart, he'll probably try to come on top. Just push him away and get him to your closed guard, once again.
And that is your simple escape from the back position.