When you're first getting started with a school fundraiser, it helps to have a group meeting to discuss goals. How much money do you need exactly, and what will that money go to? Be as specific as you can when you are listing expenses, as you want to cover everything you need with just a single school fundraiser, if possible. Do your best to be accurate with your numbers, and this will give you a clear idea of what a school fundraiser will have to do for you.
After you are clear about your targets, you'll need to select a school fundraiser that suits the goals of your group, the size of your sales team, and their intended customers. Have a talk about what sort of people you plan to be selling to. Will the students be selling to their fellow students? If so, perhaps something like a candy bar school fundraiser will be the most appropriate. If you can arrange permission for them to sell on school grounds during lunch periods, the profits from that can be phenomenal. If you feel that your customers are more likely to be people who live in the community around the school, however, then you may be better off going with a school fundraiser like the green catalogue or tea and coffee. It just depends on your situation, so take the time to think about these things ahead of time, and your chances of success will be much greater.