Here are some of the features to look for if you want to prevent being censored or locked into an online social network:

1. Does the service offer RSS/Atom feeds? RSS/Atom fees allow you to share posts with friends who are not on the same service.

2. Does the service offer an easy way to backup/export all of your files/photos in a standard, open file format (JSON, CSV, HTML, SQLIte)? This allows you to archive your data, in case the service goes down. In general, does your service follow industry standards where possible? By adhering to standards for data storage, communication protocols, email, web, etc, it makes it easier for you to port your data to alternative services.

3. Does your service offer an official API so that bridges can be built between your service and other social networks? An official API allows people who are not on the same network to interact with you, without joining the same network.

4. Are your private posts/messages encrypted, so only the people you share them with can read them? The service can't censor what they don't see.

5. Does the service make it easy to cancel service? If it's a paid service, do they make it easy to stop payments? If they make service cancellation difficult (such as by forcing you to call customer support, or making the account deletion link hard to find), the service is trying to lock you in.

6. Does your social network use patents, copyright and other legal cudgels to prevent competitors from offering similar services? If the company doesn't use legal bludgeons to stifle competitors, then you'll have more options if you decide you want to switch.

7. Is the code open source? If the code is open source, then if the people running the social network turn evil, go bankrupt, or abandon the service, you can easily go somewhere else.

8. Is the service Peer to Peer (P2P)? If you can run the app on your own computer, then it would be very difficult for anyone to censor you.

9. If the service isn't P2P, does the service make it easy to self host? To federate with other instances?

10. Does the service allow anonymous accounts? Allow you to access the site over the Tor network? Anonymous accounts and Tor support allow people who are in countries with oppressive governments to use the service with less fear that they will suffer government persecution if they post about topics the government wants to censor. It also allows helps people to avoid being mobbed/doxxed if they want to say something unpopular.