Where are some points you can do:
Create a website
This is a no-brainer: a website can inform about your project and can be the gathering point. You haven't host a website yourself, if you have the information in the web on some point (for instance on the main site for your project on a project hosting site like github), then it works too.
Have a public readable version control
This way it is easy to access your source code and therefore makes it easier for others to join.
Have a clear policy on submits
This makes it easy for possible contributors to understand what to do to participate. This could include stuff on how the code has to be formatted, which quality you expects and many other things.
Create good documentation
As you look for contributors, this primarily means developer-doc. That includes source-code-documentation, but also some documentation with entry-points for beginning contributors.
Have automatic build-scripts and automated tests
An automated build-script makes it easier to get from source to a running program. Document which tools (compiler for instance) are expected for the buildscript to work.
Having automated tests makes it easier for potential contributors to check, if they break anything with their changes.
Have a clear goal
Define a goal of your software, so contributors can check if they want to go in the same direction.
Provide communication channels
That not only includes communication channels to you, but to each other in the forming community around your project. So this includes mailinglist, forum, irc-channel, ...