"Someone made mention about weight. I am 6'2", 270lbs and as a former O-lineman in college, I carry it pretty well. However, I am actively working on cutting some weight. I run 3 miles 3-4 times a week and will be increasing that as I get closer to camp."
From personal experience, 6'2" and 270 is considered HUGE no matter how well you carry it (I'm also a former O-line guy). You may get into D-III or D-II but moving up will be tough. Anything over 230 will work against you. Good luck.
That's my experience as well.
I'm 6'4" and 230 and was told point blank by the DI supervisor at our preseason clinic that "if you get any bigger, we won't be able to use you anywhere but U". I'm at the bottom of the numbers returning to the sideline:
To answer the initial question,
I would start with mechanics.
You have to know them inside and out, so that they are second nature. I can't spot rules knowledge from the bleachers, but I sure as hell can tell when a guys isn't where he should be, when his signals aren't crisp, and when he doesn't move with purpose. If you fail the eye test, all the rules knowledge in the world isn't going to get you on the field.
As others have stated, listen, learn, and stay quiet. Take all feedback (positive, negative, or otherwise) in the spirit that it is intended and thank the person giving it to you. Incorporate the feedback into your approach immediately, if you can.
That said, the most important piece of advice I can give you is to have fun and enjoy the camp. You'll be around a bunch of people that love the game as much as you do and are interested in improving and being the best.
What more could you ask for?