As long as you dont have a faction specific mark, bond or cape thing equiped, the quickest way is through bounties. I thinks its only about 2500 rep to get to rank 2.then starting gear costs 60(?) Vanguard marks. Grinding for marks can be time consuming, but worth it. Some people say doing strikes for rep is a good way to get it, but I disagree. Even for the hardest strike playlist, you gain 25 rep, whereas you get 10 for any patrol mission. Not as fun, but more effecient imo. As for grinding vanguard marks, look up videos for farming spinmetal. You get a lot of crap items you can break for parts you need to upgrade your better items, too. If you have any more questions, feel free to ask! There's no definitive guide out there I could find, so I had to sift through a lot of random crap lol. If I can make that struggle easier for someone else, it'll ease the headache lol. The struggle is real