Do you know your deadlines?
For festivals: Set clear deadlines when working with NGOs, so they always know when something is needed from them. For example, it helps to create a central call for proposals a couple of months before your festival with a specific deadline. Also make sure, when NGOs need to hand in documents and similar during your cooperation.
For NGOs: When festivals have calls for projects, make sure to hand in your project idea in time and answer to requests from the festival team in a timely manner. They have plenty of things to organize and don't have time to wait on people. Festivals may provide you with free booth space to showcase your NGO/work. When asked in the application process how your values align with the festival's values or to give a presentation of your activation, take the time to submit something that will show the organizer that you are seriously interested.