This is a personal preference thing. I suggest experimenting with a lot of different grips. There are a few standard grips, though.
I can get into attacks from any of these if you want. Still, play around with them. Developing a good guard is about finding what works for your body type, flexibility, mindset and personal level of comfort. There's no single answer.
- Both hands behind the head.
- One hand on the back of the head, one hand on the arm.
- Both hands on one arm.
- One overhook, one underhook.
- Double underhooks.
- One arm free, the other hooking under the opponent's knee.
#3, What do you mean both hands on one arm?
As in, Shrimping out and crossing to that one arm so the other one can't reach over?
because, I can see someone raining down on me if i'm holding one arm.