Best way is to get into the industry and make the game or work for the company you want. Another way is to support the game devs that are currently espousing change and being innovative. We can highlight the professional women already active in the industry, women like Jane Jensen. They can serve as role models for up and coming female devs. Or you can devote time to a blog intended to give genuine feedback and ideas to game devs. Most of what they get now is brow beating and vitriol on this topic. It'd be a nice change for them to see something that isn't a condescending diatribe, but thoughtful feedback that takes the realities of game development into consideration. Or maybe a group of female gamers could start their own youtube channel to stream games and talk about their take on the industry. There's lots of things to be done.
Ah, so you use the old "if you don't like a lack of women in games, make your own games," argument, basically.
When most of the employees of game development companies are men, and often have been men for decades, it's hard for a woman to get into the industry. Yes, there are a few companies like Bioware, and others under EA (people whine about EA but EA's companies are actually quite inclusive compared to others in the gaming industry) where a woman has a chance at getting a job. Unfortunately, as Allan Schumacher and a few others have pointed out via articles and anecdotes, a woman with the same qualifications is often seen as less qualified than a man. Full stop.
Now, part of this is actually socially understandable, because if you're a group of guys used to hanging pinups on the wall or something, it's probably going to be awkward to be expected to change your ways once you have a lady on board. It's no longer a bro-fest. I imagine women would feel the same if they had an all-women company and suddenly they needed to hire a man. But being understandable does not make it acceptable to exclude someone based on their gender. If you're embarrassed to let someone in who isn't the same gender, then maybe you're doing something there at the office you shouldn't have been doing at work anyway (the fact that you're embarrassed should tell you so).
And, while a few women have gone into development via indie companies, or done Kickstarter campaigns, it's not that easy to succeed. For all the many Kickstarters and indie games that succeed, there are many more that don't.
Here's another thought for you - we've all been conditioned for years to think gaming is a boys' hobby. That's what marketing tells us. So, there are going to be noticeably fewer girls and young women who want to go into the gaming industry to develop something that is ostensibly not for them. And why should they? If they're not supposed to be interested in video games, why should they be interested in making them? This is probably why you see more women developers in the Sims franchise than you do in the Call of Duty franchise. There are also a higher-than-normal number of ladies working for BioWare in general, and Dragon Age franchise specifically, than for some other companies--which might have something to do with the fact that BioWare has long allowed for a female protagonist, and Dragon Age seems to be particularly popular among women who game.
And beyond that, too, to get more women into the industry, you also have to stop telling them that they naturally suck at math and science. They don't. In fact in their early years they often outperform boys in these fields, but then they are told repeatedly that this is not something girls are good at. They are even actively discouraged, if they take an interest. If you want them to appear in math and science related fields like game development, you need to start encouraging young women to pursue math and science, rather than discouraging them.
So long story short, it's not as simple as just saying "More women should be game developers."
I also disagree strongly with your previous statement that change needs to come about gradually. It's been coming about gradually--so gradually that there has been remarkably little change in the makeup of game protagonists (stubbly white men) or the marketing (stubbly white men) overall. Tonally, some things have changed when dealing with female protagonists - they no longer loudly proclaim they are just as good as the men because for the most part they don't have to anymore. But overall they are still presented more as eye candy than as characters by most companies (MMOs are particularly bad in this regard). And they are hardly ever shown in the marketing even if you can be a woman protagonist. It's like marketing is afraid that they might give someone cooties by showing a woman being the hero.
Before change can happen, someone needs to take risks--big risks. They need to put it out there and be completely unashamed and unapologetic about it. That's why the female protagonists in the DAI demos have been so important, and the trailer with Alix Wilton Reagan.