From a recent email exchange with a female software engineer (heavily paraphrased): Get to know some female engineers, if you don't already. Not necessarily a

From a recent email exchange with a female software engineer (heavily paraphrased): Get to know some female engineers, if you don't already. Not necessarily as potential hires, but as professional contacts. At that point, they may decide they're interested in the jobs you have, or they may know women who are. If they refer female candidates to you, their implicit endorsement will help your credibility. It will be very hard to hire female engineers if you don't know any.