Men and women think, and therefore act differently. As a writer, your goal is to toss in the unexpected while maintaining gender specific characteristics. Men would say women think irrationally, while women may label men as shallow. Your success in being able to realistically distinguish between the two will make your characters more believable.
Without even informing the reader who is speaking, many times they should be able to tell the gender. Women use more descriptive words and personal pronouns (I, you, him, her). A man is usually more abrupt and uses more action words. They are far less likely to interject their feelings (or someone else’s) into their conversation, while women like to include how they felt about a subject or event, or how they are feeling at the moment.
In conversation, women offer more detail and are more apt to ask questions. Men will avoid too much detail and tell more than ask. Whereas a woman would say, “She wore a pink, knee-length halter dress”, a man might simply say, “She wore a dress.” A woman is also more likely to use apologetic language such as “I’m sorry” or “forgive me for saying this, but…” while men use more forceful words and tone to get their point across.
Men are also hesitant to show emotions or volunteer to discuss them, while women are much more inclined to talk about how they’re feeling. Women are also less likely to express anger (and do so in a more passive way), whereas men are known to exhibit anger more than other emotions.
Men commonly want to accomplish a mission or task and their action brings about a result. Women often focus their attention on relationships and their reactions are motivated by emotion and feeling. The differences in each gender’s way of thinking determine to an extent their actions. When caught in a dilemma, men are more apt to do something physical to solve it. Women will try to assess the situation by discussing it with others or looking for answers elsewhere (not surprisingly, most self-help books are read by women).
To make your story realistic, try not to stereotype your characters. Your hero can be brusque and insensitive in some scenes, but have moments of reflection and intense emotion in others. Likewise with your heroine, don’t overdo her emotional side so that she is crying in nearly every chapter. Readers like to see a mix of strength and weakness in each character.