Alex, David and Brian jumped in first and they are all correct, embed
yourself in as many communities as you can and don't pitch. Even
before you follow their advice though, I'd say DON"T call it marketing
and don't see it as marketing. You are meeting people and communities
to make yourself and your space available as a cool place to work, not
selling something.

A coworking space has to be the place where you want to go to work, to
get more things done, meet people to get and lend a hand. Even though
technically you are providing a service because you do need to pay the
bills, in practice you have to see it as assembling a group of great
people to work with, it's more effective and more fun. Show up
everywhere so they know it exists, give people opportunities to build
a community in your space and to try out that space and then let it
happen. You can't make it feel like a service and an expense for an
office because that's not what coworkers look for (even if they don't
know it yet). If you market the place and sell too much, you will push
people away and/or get the "wrong" people, you'll end up more business
center than coworking.

Possible idea : when you happen on someone who seems super plugged in
to communities and a good fit for you, maybe try co-hosting a Jelly /
Cream Cheese session with that person in your space, tap in to that
network (nicely, politely and honestly).

Props on starting this without the safety net of pre-signed members,
now go forth and meet cool people! ;)