Let me start what should be a number of interesting responses...
(1) Put together a "steering committee" - a small group that is capable and willing to dedicate the time and effort to make it a successful show. Though the whole club should be involved, you don't want the whole club making decisions or you won't get anywhere. Make sure at least one of the people has experience in accounting/finance. If the show is big, you might want to have a person in charge of each area - i.e. a person in charge of the vendors and vendor area, a person in charge of workshops and demos, a person in charge of the exhibition space, etc.
(2) Put together a show plan. Decide how big you want the show, how many days it will be, and what you want at the show (exhibition space, workshops, vendors, demos, etc). Estimate how many people will attend and whether the show will be primarily for bonsai enthusiasts or general public. Don't forget a marketing plan to make sure people know about the show. Put together a show schedule with dates, times, etc.
(3) Put together a budget for the show. Make sure you have adequate financial resources.
(4) Put together a calendar of critical dates - what needs to be completed when. Make sure the team knows the dates and commits to getting stuff done. Have meetings on a regular basis to discuss progress and update the calendar.
(5) Find a suitable location. Many commercial locations (hotel, conference center) will have a lot of experience managing events and will be able to help you with basics. Other places (gardens, church basements, etc) may not have as much to offer. Don't forget to consider infrastructure that supports the show - availability of parking, bathrooms, food, lodging, etc. Make sure you have the necessary approvals and permits (if required). In your schedule, make sure to allocate enough time for setup and tear-down/clean-up.
(6) Develop detailed plans for each area of the show. For the vendor area, for example, make sure to have adequate tables, chairs, drop cloths, electricity, data cables, lighting, garbage cans, push carts, etc. Make sure you understand how vendors can unload/load their trucks, when they can set-up, when they need to be gone, etc. Make sure vendors have preferred access or parking. Talk to vendors ahead of time and get a checklist from them of things they need at the show - make sure you provide it.
(7) Make sure to have necessary extra materials at the show for surprises. These include - first aid kit, tools, duct tape, extension cords, drop cloths, garbage bags, paper towels and cleaner, etc.
(8) Develop a schedule for people to register for the show. Set up the methods for them to register, including how you will handle signups for workshops, payment processing, etc. Make sure you control show access (as appropriate) to allow public access to public areas, but limit access to pay areas. Create a similar schedule for vendors (if you have them) including how much you will charge vendors, how they register, how they select/get allocated show space, etc.
(I can add to this later - right now I have to run)
