Mario Kart Wii/Flower Cup

Mario Circuit
Use a mushroom to skip the corner at the Chain Chomp, performing a stunt as you come off the ramp to gain another boost as you land on the other side of the bend. If you have good offroad speed, you should do it even without a mushroom boost.

Coconut Mall
There are several places where you pass a pair of moving escalators. One goes in the direction you are driving, and the other in the opposite direction. Pick the one which goes in your direction to receive a speed-boost up the slope. You will slow down if you drive over the other one.

Watch out for the cars near the end of the tracks; if you get hit by one you will lose your items and a lot of time. Learning their patterns is essential for getting as many of the boost pads here as possible.

Don't forget about the shortcut near the beginning. At the point where you are given a choice between two flat roads and an escalator, if you have a mushroom, take the rightmost path and go through the store with an open door, and you'll shave valuable seconds off your time. Don't forget that the store floor counts as rough terrain, so make sure to use that boost.

Near the end, when you are close to the parking lot, always take the high road. The jump there is significantly higher and gives much more boost if you do a trick.

DK's Snowboard Cross
After you land at the top of the mountain, you will encounter a ramp, and after that some very dense snow. You will slow down tremendously in this snow, so unless you have a mushroom, star, trick boost, etc. avoid this.

Mid-way through the track, there are several small piles of snow, plus some boost jumps. Aim for the big ones if you can, because they also contain item blocks — but don't forget to do some tricks off the small ones as well.

Near the end, you will enter a half-pipe with some snowboarding Shy Guys. Avoid the dense snow by boosting at the top of the half-pipe, and don't hit the shy guys!

There are many half-pipe jumps throughout the course. Use them to your advantage, but don't forget that you should always go not only up, but also forwards, so you keep your speed while you do tricks for boosts.

Shortcuts
After the small piles of snow, you'll see a cliff to your right. If you drive off, you should land safely on the next section of the track.

Wario's Gold Mine
Stay on the track — it's harder than you'd think. Use the quarter pipes for boosts, but avoid using them while using a star or mushroom. You'll fly right off the track. Also, avoid the mine karts near the end, but if you follow their tracks, you can find a jump which has some boosts, item blocks, and a jump for tricks at the end. Just be careful not to fall off!

Shortcuts
In Time Trials, once you start, use a mushroom to jump over a lone pipe behind the finish line. Turn around and time it right to hop onto the pipe and fall down. You will be right behind the finish line. Cross it and you'll be on the next lap. Use the same method until you're done with the third lap.