Although you may feel that you can organise your event and everything within a couple of weeks, local authorities and businesses need to be informed well in advance. Early planning will give you plenty of time to carry out the important following tasks and obtain specialist advice and information where necessary.

Notify statutory authorities (i.e., local authority entertainment department, police, fire and ambulance services) of your proposed event.
Book or hire the venue where the event is to be held.
Risk assess your event and event venue.
Arrange public liability insurance cover.
Book caterers, amusements, entertainers, attractions, activities and services etc.
Advertise and promote your event to the public.
It will also allow time for voluntary organisations (i.e. first aid societies, etc) to make their arrangements, especially if they are needed to attend the event.