More female gamers = More fans = more customers so it can be only good if we can bring more.. MEA only needs to do things right in order to do so.
To begin wish, put good and meaningfull romances options, and yes among them, have an LI very conventionally attractive like Cullen, like so attractive, that almost none would find him ugly. I have seen a lot of people claiming that either Cassandra, Josephine, Sera, Blackwall, Iron Bull, or Solas was ugly, and of course the opposite. There were various opinions. It's been one year now and yet I haven't seen a single person claiming that Cullen was ugly or very meh with his appearance. ( meh only because of his personality or boring ) Even among guys. I only see people drooling over him, even those who are not fond of him. Which I find astonishing, there's usually always people disagreeing over something on the bsn, this time I haven't seen it.
What he will look like doesn't really matter as long as he is nice to watch to most folks, with a deep personality that you can explore. After to each its opinions, there will be probably other romance options. The most important it's that there is at least a romance option who is conventionally attractive, so no one can claim that they have only ugly guys. ( but there will be always people who think that way though )
Have a good and big advertising with the next femshep. A lot of customization, a very good character creator with nice hair options this time... a lot of aesthetic, Have a fair treatment in the game, make the female protagonist as badass, no more crap like Jacob cheating on femshep after I love you ( I don't see the point doing this ), equal content, as much as with male protagonist, fair animations, as good as it will be for the next male protagonist, add candy eyes with a lot of pretty male npcs, as much as with female npcs. A deep and good story to enjoy, with rpg elements, good and deep companions, a great gameplay.
Have also many female npcs, and if possible that would be nice to see many female npcs in every race, if they are supposed to exist. Like a female krogan etc; Have many female npcs with great and serious roles, with high military ranks and among the common soldiers, and everywhere in all the departments, etc.
This is what I would do with pragmatism and enthusiasm, if I was a dev. But I'm not, so I'm counting on Bioware. We'll see how it goes.
Basically, make it more female friendly, and that way, more people will be interested with every game. Everyone will be happy, everyone will enjoy the game. The female fanbase will grow. Variety is good, variety is great.
An then, there will probably much more people you could try to woo in the multiplayer more active as it seems to be all about for the op actually lol. 