The first thing you need to do is make yourself aware of all the different fundraising options there are, and the issues associated with each. Some high school band fundraising work well for larger groups and have higher minimums; others are optimized for smaller groups, with high profit margins and low minimums. Educate yourself about things like shipping fees and other requirements before you make a final decision.
Usually, high school band fundraising events will involve contacting a fundraising consultant. This person is there to help and inform you, so make the most of it. Ask all the questions you need to ask about your high school band fundraiser, and make sure you know important things like when the orders have to be turned in, and when you can expect the products to be delivered.
Most of all, have fun with it. There are a lot of great high school band fundraisers out there - it's not all just chocolate bars anymore (though chocolate is certainly available if that's what you've decided you want!). You can choose anything from scratch cards to pretzels... really, the sky is the limit. Some high school bands are even choosing to do green fundraisers, which work like the other fundraisers, but involve products that help the environment. People get really excited about it, and as long as you can keep that excitement up, everyone involved with your high school band fundraiser is sure to end up a winner.