You can get all sorts of new sides to both the fandom and the anime if you interact with the official social media, such as seeing exclusive illustrations for merchandise before it comes out.
Note of advance warning: Since this is originally Japanese entertainment we’re talking about, you might need knowledge of Japanese to navigate these things.
For this, I’m going to use the Boueibu (Cute High Earth Defence Club) series as my main examples because they’re the ones I know like the back of my hand, but I’ll try to write as generally as possible so that it can apply to most, if not all, cases. For non-Boueibu cases, I will state the fandom I’m using.
Generally, the easiest place to start is with the official website. The website normally has a bunch of handy links which you can use as a starting guide for finding official merchandise, the OP/ED streaming links on your platform of choice and so on. Digging on certain sites’ “Special” sections may get you wallpapers or social media icons.
Googling up the official website should give you a single Japanese-language link which should be the one, or less commonly, an English-language one (which is the case in the Boueibu example as of this time of writing – the corresponding Japanese website is this one). Generally, English-language websites don’t get updated much outside an anime’s run or disc release in the region they apply to – generally English-language websites are tied to American licensors and so they’re often tied to licensors like Aniplex of America. In the English Boueibu site’s case, it’s likely tied to one of the producers, Pony Canyon, who put out the English release under their name.
Twitter is where a lot of official anime accounts tend to congregate. This is because Japanese, with kanji and shorthand for certain things (e.g. a deadline – such as the ones for preordering discs or merchandise – is a shimekiri/締め切り, which can in turn be represented as 〆切), is much easier to cram info into than it is in English with 120 symbols.
Generally, official anime accounts are indicated by the characters 公式 (koushiki), meaning “official”, in either their description or their name, or by “off” (again, short for “official”) in the handle.
Less common are official English-language Twitter accounts (e.g. the Boueibu one), which have much of the same caveats as the websites, or official accounts on Instagram, Line or other social media sites. In rare cases, you can find in-character content, such as this account for Ritsuka (from Given), or even April Fool’s Day content.
For discussion hashtags, AniList has their own section in the database for that or you can consult Yatta-Tachi‘s list of anime hashtags (which is not up-to-date with fall 2020 as of the time of checking it).
Voice Actor/Staff Accounts
For Boueibu, I got a lot of behind-the-scenes information from director Shinji Takamatsu’s Twitter. As of the time of writing, that Twitter is on hiatus so I won’t link it though.
Voice actors are very much their own world which I have discussed to some degree, but I confess I’m no expert on. Voice actors and staff have various roles on just as many anime which you might not want to know everything about, so in this case you might have to be selective. However, if you stick around long enough, you might get to see exclusive illustrations to commemorate an anime airing/disc release or pictures of voice actors going to events/location pilgrimages (e.g. Sho Hayami, Ryuichi Kijima and Kento Ito – a.k.a. the voices for Matenrou in Hypnosis Mic – visiting a shrine, much like Matenrou do in episodes 1 and 3 of Rhyme Anima) which relate to your spheres of interest.
Some staff/voice actors just use their accounts like ordinary people, so they’ll tweet mundane things like food or pet pics. Others have a group account and include who wrote the tweet in brackets (like this voice acting company, Dandelion).
…I know, it’s not social media per se, but some anime use these outlets for their OPs, EDs and soundtracks. If you’re lucky, you might even get access to character songs.
If you’ve never tried typing in Japanese on Spotify and know how, you might want to try. For instance, let’s put 防衛部 (Boueibu/Defence Club) into the search bar and see what we get…
Bingo! Zettai Muteki Fallin’ Love is the OP for Boueibu season 1, sung by the Chikyuu Boueibu or Earth Defence Club (hence the top result/artist).
Sometimes, you get really lucky like this and the English translation is understandable, even if the content itself is still in Japanese. Sometimes…the translation isn’t as good as it could be, or it just doesn’t exist.
So that’s a really short rundown on how you can go beyond just watching the anime or reading the manga. Of course, the list doesn’t cover everything in existence, as there are specialised websites/web pages/social media channels for collaborations, anime articles and so on which are more of a case-by-case thing. For manga, you could follow the publisher, author and/or licensor and see if they have special behind-the-scenes content.
Update: Forgot to link the English Boueibu twitter…