The most important rule: stay in touch!
Nothing is more frustrating for a backer than hearing nothing after the campaign ends.
Best practice no. 1: a thank-you email within hours of the campaign ending, with the next milestones.
Best practice no. 2: share the project's progress. You have your prototype, you're going into the recording studio or starting production of the rewards? Share it with your backers to show them the project is moving forward.
This is essential if there's a long gap between the end of the campaign and the delivery of rewards.
Also treat them to sneak peeks or exclusive announcements. Your project is coming to life thanks to them: it's another way to say thank you.
Best practice no. 3: transparency! A problem, something unexpected or a delivery delay? Talk about it openly. Your backers believed in you and want to see the project happen: don't leave them in the dark or keep them waiting without telling them why.