A) Hope you get some good jobs on your team.
B) Don't commit to all-ins unless you are absolutely sure the rest of your team will follow.
C) Mark priority targets for your team with markers to help with focus, usually focusing down the healer, especially with healer is SGE(It has massive damage), when it's SCH I try to focus down the ranged DPS or Caster since SCHs take a really long time to die.
D) Play a job you are comfortable with. I find Dragoon much stronger than Ninja but my best results are always as NIN since I basically work on pick offs.

That's what works for me at least. I am Gold 1 right now but steadily climbing. Some matches are just guaranteed losses though, depends a lot on party composition because the balance is awful right now since it just came out, so don't stress over that.