1) Location - do you have the right permission in place from the land owner and the local council? Does it have the right fencing, what will you need to set up?
2) Costs - are you aware of all the costs involved? Paying for the location, ensuring you have the correct insurance such as public liability - do you know what limit you need and where to go, employees, set up kit, transportation costs, marketing fees; permission fees; have you considered getting sponsors?
3) Sponsors - put simply, sponsors get advertising at the event in exchange for payment. You will need a good sponsorship agreement in place to cover all bases and so each party knows exactly what they need to do and what their rights are.
4) Arranging the program - do you have a good idea of the order of the events and something in place for when things go wrong?
5) Have you arranged hospitality and catering? Use someone with a good reputation, you do not want your event goers getting ill ! What about portaloos?
6) Ambulance and health and safety procedures must be adhered to. Do you know what these are?
7) Jump judges, how will you find them, are they volunteers, what will they receive?
8) Marketing the event and associated costs, how will you get the event name out there? You need people to enter to ensure you cover your costs.
9) Signage for the event - advertising and around the event;
10) As mentioned above, you need insurance. This will need to cover damage to the location of the event, public liability i.e. if someone gets crushed by a horse, insurance to cover cancellation or abandonment of the event, employee insurance in case an employee gets injured.
There are a huge number of things to think about. If you need any help or advice, please do get in touch, I have a number of helpful template agreements that can point you in the right direction and get you started - firstname.lastname@example.org