Organization is key if you want everything to run smoothly. There are different people in your school PTA with different strengths, and you should take advantage of this when deciding on roles for your school PTA fundraiser. Instead of having everyone trying to help out with everything, assign roles based on who knows how to do what.
For example, I'm sure you know exactly which person in your PTA is the motivational speaker. This is the person who should be in charge of introducing the school PTA fundraiser to the kids. There's also probably someone in your PTA who is good with accounting, and that person should be in charge of keeping track of the money for the school PTA fundraiser. If you assign two people to this job, not only will it keep away any doubts about honesty during the fundraiser, it will be a lot less anxiety than having just one PTA member dealing with the whole thing. There also needs to be someone who will keep the teachers informed about what is going on with the school PTA fundraiser. The teachers have an almost constant connection with the kids, and so they are an important aspect in the fundraising process.
As you will find out, there are different roles that need feeling during various parts of the process. Giving everyone a job that suits them keeps your school PTA fundraiser team happy, and it helps the fundraising run more efficiently. Efficiency and organization are two of the most important factors of successful fundraising - get those right, and the rest of your school PTA fundraiser will come easily.