One thing Fog Creek did was we hunted harder for qualified women applicants, which meant we actually had to go to female tech recruiting events.
The problem is that there are few female developers to start with, and they are all heavily recruited by large software companies (Google, Microsoft, etc) already. The larger companies have big budgets to devote to this and encourage the very small number of women developers to go work there.
If you just sit back and wait for more women to apply, they are going to get picked up by the bigger companies before you even get a chance to interview them.
It's also difficult to attract that small group of women devs to apply to work at your company when there are no women developers there currently. The larger companies already have a bunch of women developers, so it can suggest to future candidates that these companies are great places for them to work (i.e. they won't be discriminated against at these companies). It may be that your small company is also a great place, it's just that you don't have any women to vouch for that.
So in Fog Creek's case, we increased the number of women applicants by making it our goal to get more women to apply. That's the only thing we changed. Our interview process stayed exactly the same.