Mario Kart Wii Help?

I know exactly what you mean. I get so frustrated. I will be doing a grand prix cup, finish 1st the first 2 races then then next 2 races i get hit by every power up in the game finishing 5th or worse. It just makes no sense. For the bullet, it depends how far back you are from the other racers. I like Warios Gold Mine, one of my favorite tracks. Rainbow Road is ehhh. I use a light kart so i keep getting knocked off the sides by other racers. Usually i power slide all the corners, but on RR i take the corners slow and it helps cause others fall off as well.