There is so much to see and so many people everywhere at the fair, moving in front of your camera, bumping your tripod that it will be hard to concentrate. Relax, slow down, keep in mind that it will be busy and enjoy the hustle and bustle. First thing is not to rush your photography. Bring your gear (backpack) with maybe one camera around your neck ready for that unexpected image, that special moment when light, color and visual design all contribute toward making a great photograph. Scout out the fair or festival looking for the best angles to shoot from. While scouting the fair, your thinking of where you want to be at a certain time of day. Would this be a good subject at sunset, should I use a tripod and use slow shutter speeds, or maybe this subject will work up against a blue sky. At crowded events where there is lots of foot traffic its very important to look for natural barriers, such as a column or wall or even a garbage can, where you can stand or set up a tripod to take pictures from, and not have to worry about being run over by spectators. At night try and pre-visualize what the rides will look like when you use slow shutter speeds to capture the motion of the bright colorful lights.
At parades I like to get there early and shoot images as the performers are warming up. This way I can get in closer and look for detail images and expressions I wouldn't have been able to get if they were performing and moving along the parade route.