Read Arts Council England: Action for Access toolkit.

ISAN Access Toolkit
The Independent Street Arts Network (ISAN) Access Toolkit is packed with useful information, and examples of ways you can improve access for Deaf and disabled audiences at your festivals and events. All areas are covered, from marketing to facilities, from stewarding to programming and much more.
Many of the measures you can take don't cost a bean, and all of the advice in the toolkit will help you encourage attendance and improve access for the audience members you might not even know you were excluding.
Download your copy of the Access Toolkit at www.streetartsnetwork.org.uk