The best way to rank up quickly is to play warzone mythic ( which is only available on the weekends) and if that’s not available, turbo or legendary would be next. Make sure you play with gambit legendary boosts and if you don’t have any of this just use plain legendary xp boosts. Another AMAZING way is to do a little trick call quick- coring. You basically have to group up with a good fire team and capture all the bases, immediately after that go straight to the enemies core. Doing this takes about 5 minutes and you get massive rewards (up to 20,000+ Xp, if you’re using boosts.)