This is a strange maneuver but worthwhile to try. When you start any given race, allow yourself to fall into last place. Then, grab an item. Because of your last place status, the game will give you an exponentially higher probability of grabbing a great item (like a Star, Bullet Bill, et cetera). Then, work your way past the last place players until you’re in third or fourth place and use your good item to make your way towards first place.