Don't put two frat boys with a very shy girl. Some people prefer to make same-sex groups, but that's very transparent to the students. It also isn't always possible. I prefer to figure out personalities, and pick a nice approachable guy or two to work with one or two women. Vary your examples and conceptual presentations.
Different people learn in different ways.
One may be a visual learner, one may be a mathematical learner. Different presentations of the same subject will help everyone learn a topic better. Switch around your gender pronouns. Also check your examples. Use examples that are applicable to both genders.