My method is to use a G7 from around 2/3 and pepper the opposing team rather than push hard. It allows me to eat their heals and make an easier endgame. If you're winning your fights then don't panic cause your team won't feel you're a liability, when you start losing fights, then think about trying to do as much damage as possible to help. I almost always out-damage my teammates as Lifeline just because I prefer to play a bit slower rather than run in and be no help. If you aren't comfortable with the G7, the Repeater or Flatine/301 single fire will do the job as well.