I replied to a question on Quora a few months ago - What are the *unofficial* rules of Tumblr (and what ought they to be)?
"Conventions, courtesies, credits, comments — what are the spoken and unspoken rules of the Tumblr community? Where is the community deficient and where does it excel?"
Here’s my take:
1. Be interesting
Have a point of view and add something to your posts - pull out what’s interesting about the argument, connect it to another idea, or just explain why you like it. Give people a hook to engage with to inspire questions or reblogged responses
2. Be honest
Text-based Tumblr likes personal accounts, confessionals and the exploration of personal vulnerability. (It’s the closest thing to the Heir To LiveJournal out there.) That doesn’t have to be your thing, but it’s definitely not a bragging, self-promoting kind of place.
3. Promote your friends
If a Tumblr or Twitter friend has written something good, give them a boost. Pro-social behaviour is good for community-building.
4. Credit your sources
Not widely done, but should be. Use both the linked URL and the body text to credit who made the image, what it’s called, and their website. (Don’t know? Use Google Image Search or TinEye.com.
5. Don’t be an asshole
Tumblr’s probably more sensitive towards sexism, racism, transphobia etc than other communities. Being a bigot isn’t cool.
ETA: Imperfectly phrased. Obviously don’t be a bigot because it’s wrong and hurtful, not because you’re concerned with “cool”. But, yes, community norms mean you ain’t going to be cool on Tumblr if you’re a hater.
What do you reckon?