This party was for the kids, by the kids. With parental oversight, but the goal was for the children to learn by doing.
1. Set a date and time. Set an alternate date in case you are unable to procure a meeting place. Hint from experience: don't choose the Friday or Saturday just before Christmas.
2. Decide on the approximate number of people that will be invited.
3. Based on that number, reserve a building. A local church, community center, or VFW Hall may be possible sources of inexpensive rentals.
4. Set your budget -- in stone. If you set an approximate budget, it will run over and over and over. Set it once and stick to it, even if it means making do in some places. Decide who will fund the budget -- a set amount from each family? each family according to its ability? money from a previous fundraiser? each committee funding their own expenses?
5. Decide who will be doing what. Typically, you will need the following committees: decorating, entertainment, food, invitations. Let an adult chair the committee, with children choosing on which committee they will serve. Even very young children can participate. You might also want to designate someone as official photographer.
6. Let the children divide into their respective committees and begin planning! The adult chair oversees their planning (helps them budget their time, money, etc), but the plan is for the children to make the choices and do the work.
Some committee chair hints:
Invitations -- If you have a color printer, these can be done very nicely on a computer. Have one person receive all the RSVPs, regardless of whose guest is responding. Send invitations to everyone in your homeschool group, too. It is a nice gesture, and a good reminder of the time and place