What techniques can be helpful when playing Mariokart Wii?

OK, I just got Mariokart Wii a few weeks ago. I am getting pretty good at the game. I've figured out a few simple techniques from the manual that help me do better. But still, I probably need some more ways to do better in the game. So what do you think? What techniques can be helpful when playing Mariokart Wii? How can I survive items such as the POW or the spiny shell?