How can my team get better at gb matches on mw2 (specifically SnD)?

i have a 2v2 team and another team that plays 3v3 and 4v4 but we r never consistent...im more worried about my 2v2 team cause we r both really good but we just started our team so will we get better at gbs eventuall?? also what can we do to practice and if u have any class suggestions let me kno...Thanks