I would just focus on making it a constructive open environment where everyone feels welcome (irrespective of age, gender, or ethnic background).
I think the gender gap will surround technology for a little while longer, and I could write an essay on why that is (and what can be done). But I won't.
I would be careful with walking the line between being accepting of female inclusion and making them feel like they're VIP members who nobody can treat as equals as a result of their imposed "status." Such status can easily flip (i.e. "good" and "bad" statuses are both exclusionary).
I've seen several organisations who were typically male heavy attract female members, and it was always a slow grind which just essentially involved treating everyone like equals and with respect.
I would avoid trying to over-respect women too, since that breads resentment and sexism. It is also kind of condescending (i.e. "well I don't think you could get this on your own, so I am giving it to you").
So if you want to get some female speakers then make sure they are up to the standards you expect from their male counterparts, doing anything else is more than a little counter-productive.
PS - Also maybe come up with some basic speaker guidelines to make it clear that sexism, racism, etc (even as "jokes") are not acceptable. This might be "obvious" stuff but it still might need to get said.