You just need to let the game run. I done this a few times when I had a big backlog of cards drop after or during the seasonal sales. You want all your drop ASAP because you don't get boosters from games with drop left. By selling the valuable card drop and booster drop and keeping the cheap cards for crafting you can level up at a decent pace.
from reddit: the front page of the internet http://ift.tt/Rf7ejr