It's not just the accordion either. If you are hanging on for dear life and the guy in front of you is doing the same and blows, he has to pull out which leaves a hard gap for you to close. If I'm hanging on the back of a real fast group, that's usually the way I lose them. So be realistic about your fitness. Don't mess things up in the front if you can't hang, but don't ride at the tail end either if you think some other guys are worse off.

I will add the same advice just hang in there and enventually you will not get dropped. Also listen to the advice about riding smarter this makes a big difference. I know when I started I would find myself on the front right before the sprint zone, then everyone would take off and I would be gassed from pulling and have a hard time grabbing the tail, next rides I made sure I was off the front and rested before the sprint. Take short pulls or just rotate through if your getting tired, no one will mind and it is better than trying to pull too long and dropping the group pace because you are tired.

No hill advice from me.