There isn't really much you need to do to "maintain" them as a user. Most of the work ends up needing to happen on the author side, but you can support authors with that.
Some things that come to mind:
- Keep your addons up to date. Especially when a new DLC or chapter update was just released. Most issues that get reported are due to outdated addon installations.
- Check the addon comments of the ones that didn't receive any updates after a new game update and disable or uninstall any that are known to be incompatible with the new game version.
- Don't use addons like BugEater that sweep problems under the rug. They often make it hard to determine the actual issue.
- Instead try to collect steps how to reproduce errors you get and report them to the authors.
- Bonus point if you add a LibDebugLogger logfile as described here.
- Write a positive comment when you like an addon or a new feature that was just added. Usually we only get to hear from users when something broke or there is a complaint or they want something added, which gets really demotivating and tiresome after a while when it's the only kind of feedback you get.
- Donate to your favorite authors (in case they have added a donation pages). They spend countless hours on making them and keeping them working with the sometimes big changes that ZOS makes to the game for no personal gain.
- Check the forums regularly if they need help with anything. Sometimes authors ask for translation help in the translation forum or for testers to try a new feature.
I'm sure there are other things too that would help that I didn't think of right now.