One thing we can all do is send letters of encouragement to women to join wikipedia. I don't know if there is a form letter already used that we can merge ideas like the below into. This is includes and expands on points I sent out to a couple of political women friends and womens lists - about 150 women total - as a personal encouragement. Underwhelming two responses so far: "good idea" and "I'm too busy." So I know that the letter needs work! Maybe we could have a couple versions linked from http://meta.wikimedia.org/wiki/Gender_Gap
Revised draft version:
Wikipedia has set as it's goal increasing the number of editors from under 15% to 25% over the next few years. See the New York Times and other articles and other relevant Women and Wikipedia links here. http://meta.wikimedia.org/wiki/Gender_Gap
I've been editing a lot the last few years. It is fun for amateur policy wonks and has taught me a lot about good referencing and how easily ones own biases can twist the material one is dealing with. And it's a great motivator to learn more about a topic you are interest in - you go in and improve an article on a topic of interest with better information from better sources.
And it's fun to get challenged, whether you are proven wrong, proven right, or work with others to come up together with a collaborative solution. Talk page discussions and debates are a great way to learn about Wikipedia editing policies.
It can take a few months to get up to speed on all the policies to enable you to edit effectively, i.e., making edits that will stick while deleting unsourced and biased material.
Also, since Wikipedia is still mostly a 20 something man's world, it may be best to use a gender neutral name and not advertise on your user page you are a female, at least until you get the hang of editing it. At least avoid using use your whole real name to avoid possible harassment on and off Wikipedia.*
But if you have favorite topics that you'd like to see better covered, have time on your hands (as some of us semi- and retired women do), and want to have some great fun, do try Wikipedia.
(*CM Note: this point is actually said explicitly in User name policy, but few people get to it before they choose a user name)