oh true, if you go through Greenlight first, then you do get some more exposure, since the game will be on the frontpage for a bit longer than the normal steam pages. But the attention you get there is mostly yes/no votes (literally a 50/50 divide for most games I know about).
Having some sort of sign-up or even a beta to try out might increase your results more (haven't tried that myself).
Twitter and facebook are two good ways for marketing, Twitter is mostly interesting for the quick news posts (any thing like new screenshots, blog posts, etc) and hope it get's retweeted/favorited enough.. and facebook is best for trying to grow your fan base, getting people to like your page so it's easier to reach them in the future.
Also try to setup a mailing-list and see if you can push people to sign up on that.. nothing beats having a direct line to your customers.
reddit is a big mystery.. most links,posts seem to just die in a void, at least on all my attempts
but if it DOES get picked up, it goes big pretty quickly.