Tournament rewards are based strictly upon the leaderboard, so give it all you've got to rank as high as possible.
Players who climb to the top of the leaderboard and claim the highest ranks will earn huge prizes of Diamonds. You can check out the current Grand Prize on any given Tournament's page, and pressing the more prizes button in the corner will allow you to see the full breakdown of what ranks are receiving which rewards!
Please note: Money won from tournaments do not count towards your World Tour Progression.