swiperPay attention to what the rest of your team is doing--if you're by yourself there's a good chance you're overextending (or they're massive vaginas, but since you're new play more passive and stay alive until you get enough experience to know what's going on). Try to stay with your medic, but behind the pocket and don't take too much unnecessary damage.
So are there specific times when the Demo does lead? A Kritz situation?
Is a demo still the main sentry-buster in a HL game, or is it a focus-fire situation like 6's?