Upworthy follows all of these rules.

Title is super important:

8. Make sure your headline is compelling, a call-to-action or a list - We talked a bit about the need to make your title catchy. In an era of RSS, Twitter, Facebook & new consumption tools like FlipBoard – titles matter.

It's okay to tweet multiple times:

And I tell people all the time, it’s OK to Tweet more than once (full advice in this link). In particular I do an East Coast morning Tweet (5.40am PST) and a West Coast Tweet (8.40am). Each converts the same (e.g. if I hand’t sent the second tweet I’d get a lot less clicks / shares). I use a tool to set it up in advance so I don’t actually have to be ready to Tweet in real time.

Skip slide shows -- put everything on one page:

Give up page views – Many websites give you presentations or lists and make you scroll through 10 pages to see the entire list. Jon says don’t do this. You get a few extra page views but less people will consume the content and certainly less will share it and make it go viral.