You can find many shortcuts in this game.  #1.on Koopa Troopa beach, first you might need a mushroom or a star to do this.  On where the 3 ramps are, wait for the last one where the little tunnel is, now use your mushroom and aim for the tunnel.  (You might have to jump). #2. on Koopa Troopa beach, again on the last part where the 2 ramps are, go on the sandbar and watch out for the crabs, you have a 50% chance that you will be in first if you are in second. #3. on Rainbow road, right after the start (or finish), the big ramp is there, jump then turn left (right in mirror mode), (you want boost to make this easier), and then hold the control button to break.  After that, you will be on the later part of the track.  #4 (last one) two little shortcuts together on DK's jungle parkway, on any lap, where the big ramp is, jump then turn left (right in mirror mode), you will be on the skinny road. After that shortcut, when you go over the bridge, where the cave is, go up the hill and jump consolingly to get up the hill and you will have a 60.5% chance that you will be in front of someone.