Half of the people in the world are women. Depending on where you are, that differs by one or two percentage points. Males have a slightly higher chance of being born, whereas females have a bit longer of a life span. Unless the place where your characters live kills off most babies of one gender, your book should also reflect that. We’re mostly getting past having a token female, but having three guys to every one woman is hardly better. If you have too many men (or too many women) in your book, just change their genders. It shouldn’t change their personalities at all.
This is an excellent post, and brings up great points about the likelihood of women, ethnicities, non-traditional sexuality, etc. But I have to disagree with this excerpt on the ‘changing their gender won’t change their personality.’
It depends on how developed they are as characters. You can get away with that for the 2nd & 3rd tier characters, but if it’s one of the major characters whose backgrounds and personality are going to be explored in the story, then being female vs. being male almost certainly does change who they are. Their experiences will be different. Their perspectives and priorities may be different. The nuances of how they engage and interact with other characters will probably change.
In other news, DFDwritingworkshop is a pretty nifty Tumblr if you write. Some great resources and things to think about.
DFD’s Writing Workshop: Some ratios to keep in mind