A brief guide to basic rules and terms of fandoms
Fans should be seen but not watched
One important facet of fandom is making fans feel seen, but not constantly watched. Basically, this means that fans' opinions and needs are valued and acknowledged by a brand, but, at the same time, that fans are not feeling as if the brand is keeping total tabs on the fandom at large. It's a difficult balance to walk, but a neccessary one.
Transformational and affirmational fans
In Fandom studies, it's often useful to divide fans into "Transformational" and "Affirmational" fans.
-Transformational fans mold the text to suit their own desires, re-contextualizing the basic text with different settings, characters, and themes. They often create fan works that are less concerned with accuracy, and more invested in mirroring a base theme or concept of the original work.
-Affirmational fans find allegiance to the source material the ultimate act of fan devotion. They often create fan encyclopedias, note-perfect cosplays, and fan works that closely resemble the base text.
While fans don't want to feel as if they're being watched, they absolutely appreciate a brand acknowledging their loyalty/ depth of fandom. The trick here is knowing when they want your involvement. If a parent brand is being tagged in a post, it's usually safe to retweet/reblog/et cetera the post to acknowledge the fan's dedication.
Crediting is a credit to your brand
When retweeting/reblogging/ et cetera fan art/fanfic/fan works in general, make sure they've solicited your brand's involvement AND be sure to credit the original creator. This small action endears the brand to the fans, and makes them feel seen.
Providing avenues for engagement
Whether your fans veer more towards the Affirmational or the Transformational side of things (and it's best to think of the two terms as poles, rather than disparate concepts), a central job of a brand is to provide fuel for that fandom fire. That can involve GIF-ing shows, providing behind-the-scenes moments, or even just stand-alone artwork that your fans can use as logos and desktop images.