First Concert Questions...?

o my friend and I are going to the Green Day concert in Minneapolis and we have GA tickets. How early should we arrive if we want to be as close to the front as possible? Concert starts at 8, doors open at 7. Also, how bad are the mosh pits at Green Day concerts? Like, what are my chances of being crushed? haha. I'm 15, 5'6", and skinny so I'm kind of nervous. Oh, and any tips for me? Besides the obvious don't wear flip flops/a skirt/ dangly earrings/ etc? Thanks. =]