Create a NG+ Saboteur (Level 15, World State 2) and finish the first 2-3 missions in Barrow (preferrably on easiest difficulty). Now switch between the lobby screens of those 3 missions for any lobbies on Legend (or Master, but it's not as effective), preferrably mission 2 ("The harder they fall") as it nets you tons of XP and loot fast. Join the Legend Lobbies and follow the guys who are killing everything (you barely do any damage so evade enemies instead of attacking!).

You will get tons of XP and will probably hit level 30 within 2-3 minutes. Then continue joining Legend Lobbies (only switch between the 3 Barrow missions!) to get your Hero Levels to at least 150. While doing so you should get all loot (and salvage everything below purple rarity; keep all cores!) and try to destroy respawn beacons without dying as every destroyed respawn beacon gives you a loot bonus (chest symbol in your buff bar) up to 3x (3 chest symbols) but you lose them when dying. So without dying and 3x loot bonus you should get rare stuff way faster and more often and also get a HUGE bonus to the final chest on the evac helicopter (tons of cores + awesome and rare weapons)!

Your goal is to get a legendary Energy Gun and legendary Plasma Shotgun with at least 8+ core slots (12 is the highest and best) and a legendary Vortex Grenade with preferrably a fast charge ability. Restat your attributes to at least 80% of the bar and if you don't have many slots that give you core bonusses, try restatting them too (you can backup your save on USB/PS+ before doing so and re-download it if you don't get good slots!) and fully fill both weapons with rank 3+ cores. For the Vortex Grenade you ONLY want to slot blue and yellow cores! <good slots for Energy Gun and Plasma Shotgun will be added soon; Guide will be continued>