Couple of tips. When first starting you want to save all your upgrades you earn completing quest to upgrade your most powerful character which I would save till you acquire a blue rare or better.
After that u can use the blue rare or better to mine gto coins for free! U dont even have to keep the game open. Literally free money
White platform = common green=uncommon blue=rare purple=super rare yellow=legendary.
just buy out all the cheap ah whites and greens. It is the fastest way to easily complete that quest. Not to mention if you do 250 trades you get 5 gifto for free.