Replay previously completed stages and farm them for more coins. Repeatedly play stages while doing lots of tricks.
To unlock your next destination you must finish a race in first place. Upgrade your tires as well as your inverted castle and play the final stage again.
To get more trophies, get a perfect landing. Do not do a lot of tricks to minimize your failures from landing. Tricks will also slow your racing time if your goal is to finish first.