So i found that playing the story mode and only doing those missions while using boosters will help you get a lot xp. 5 xp boosters will net you a ton of xp and doing only the main missions will help even more. I also suggest doing the treasure rooms. Now the xp boosters are great, each one gives you 30 minutes of xp boosts and 5 will give you 2 and a half hours of boosts and 200 percent more xp. Just remember 5 is the max for xp boosts after 5 you get the time but not the xp. So 200 percent xp boost is the max but that is all you need.