Twitter actually tends to go better if you DON'T try to be entertaining or witty. Just follow a bunch of people who are either interesting or like similar things that you do (try for like 100 at first). I follow a lot of news sites, cartoonists, gamers, celebrities, etc. The higher number of tweets you have coming in, the more opportunities you have for sending a reply about something, or retweeting things you thought were interesting. And the more you do that, the more likely someone with similar interests will find you in a keyword search.
I kind of struggle with Tumblr and Facebook partly because it feels like there's more of a formal requirement for content. Whereas with Twitter, that 140 character limit means no one expects me to write anything particularly intense or in depth. I'm just like "Hey Guys, I'm working on stuff and watching Dollhouse. Man, I love Victor. La la la." And then Dollhouse fans find me and hey, we have something in common! :)
I do actually enjoy the social media stuff to an extent, but juggling multiple accounts can start to feel like a chore. I can understand why people often hire others to do this stuff. o.O