Waluigi Stadium
After the second boost turn right, there should be a puddle of water, go on the wall and you can cut across the whole turn, this works best if you have a mushroom handy.

Luigi's Circuit
You will need 2 mushrooms for this. When you see the chain chop go on the grass right behind him, use a mushroom to go across half the grass, right after you passed him, use another one.

Mario's Circuit
You will need 3 mushrooms for this. When you see the first tree after the first turn go behind it and use a mushroom, when you reach the chain chomp use another one, right when you pass the last tree, use your last mushroom.

Yoshi's Circuit
You will neeed 1 mushroom for this. After the second turn you will see a a turn and a hill, boost over the hill with your mushroom and you will skip the turn, this saves alot of time.

You will need 1 mushroom for this. When you come out of the tunnle, you will turn once, there is a bump right off of the track, if you turn to the left after you hit the bump, use a mushroom, you will be in a under ground tunnel that leads to the turn with yoshi's shell.

DK Mountain
You will need 1 mushroom for this. Right after you pass the start/finish line, there is a turn with a small block of grass in the middle. Use the mushroom right before it, you will skip the turn and most likely fly very high in the air taking the lead.

Dry Dry Desert
You will need 6 mushroom's/1 star/1 golden mushroom for this. Right after you pass the start line, there is a huge plain of pure dirt the cuts half the track that doesn't have any dark dirt in it. Use your item needed across this whole plain destroying the race with you in 1st.

You will need 1 mushroom for this. When you pass the second turn, there is 3 turns. After the first turn, use a mushroom, cuting across the dirt.

Mushroom City
You will need 1 mushroom for this. Right after you go through the first tunnel, go straight, there should be a ramp of dirt that you can use your mushroom for. Go ahead and use it right when you hit the dirt, that way you fly right over that whole part and land on the other side.