I had to think about this one and the only thing I can come up with apart from how they dress and their quirks is –
Give the characters reasons for their actions.
Example no. 1
She felt sorry for him because he stood alone at the wedding and didn’t look as if he was enjoying himself. He was part of the family now and it was selfish of any woman to ignore him. She had been drinking too much wine and apart from that he was attractive so she asked him to dance.
Example no. 2
He picks up a woman in a bar. She’s keen to talk to him because her husband is watching football on the television and drinking with his mates. She agrees to go for a spin in his car for half-an-hour because she knows him through buying The Farmers Weekly in the paper shop. And she’s flattered that a farmer wants to spend time with her.
Example no. 3
A woman welcomes her gentleman friend into her home. He breaks down and tells her that his wife has been found murdered. She tries to console him, but he’s inconsolable. He doesn’t know what’s worse – his wife dying or being told not to visit anymore because people will talk.
Each example tells you something about the character. In the telling of the story, facts are given which illustrate reasons why people act in the way they do.
The big question is – Will their actions make them memorable?