If you don't care about what armor or weapons you're using, you can do a lot of Public Events or Strikes to get the tokens and rank up with the Vanguard. I would suggest doing a lot of Menagerie or Vex Offensive while it's still available, because the weapons from both are solid and you'll have access to better roles for weapons that will make newer content easier to do. I'd rather have a well-rolled Austringer for the campaign than a blue scout rifle.

Run strikes and you'll power up to 900 very fast.