build uber often! if ur constantly building uber, at a low level, you'll have a better chance of surpassing the enemy gamers.
how do you do that? get a scout who's running the basher/sword to hit himself while u both sit far back in a doorway ready to run to the previous control point. tell ur team to not take damage or big fights (they don't have heals)
if you're building u shouldn't be healing anyone other than your scout. it's ok to arrow or give buffs to ppl with crit heals. for example, if a retard roamer with 180 who's actively fighting comes to you for 300, ignore him until he's got crit heals
your team can disrespect you for being new, but remember that ur the one with the medi gun. you're the girlfriend who says no in bed if the guy's always playing cod on his xbox. this does NOT mean to not listen to your team. if your team has a more experienced player or a skilled maincaller it's ok to listen to him.
also sit in spots that are hard to shoot or bomb. corners not in a chokepoint sightline are good. high ground if your team's around is good, too.