Toad Circuit
After the first left turn, you will find three coins. After that, you'll find two more triplets of coins and a ramp with a blue tip (this only appears in the second and third laps). The blue tip means that when jumped off, you glide. If you don't take this, choose between one of the two passages under the bridge. If you do glide, try to get as many of the coins in the air as you can. Next, you're in a tunnel. Swerve around the dirt* and get the coins. Choose whether to turn widely and get the coins or to turn tightly and get to the other side faster**. Then you're at the finish line. Repeat two more times.
Shortcuts
*Instead of swerving around the dirt, use a Dash Mushroom to jump off the ramp. Don't forget to press 
when jumping off.
**You can also use a Dash Mushroom to cut off the turn. Just make sure you don't hit the pipes.