Short answer:
1. practice
2. aerodynamics
3. training

Longer versions:
1. At that level, everyone has pretty much the same skill set when it comes to bike-handling. In other words you don't have to worry tooooo much about the guy next to you doing a bone-head move. Everyone is stable on the bike, can hold a line, and doesn't freak out if there is some bumping.

2. As you ride more, your back and abs become stronger. You might find yourslef wishing for a more "stretched out" position over time. "Nice flat back" is the desired position for racing.

3. Best way to become a better climber? Climb more hills. Then go out and climb some more. Sad but true!