Stick with basic, muted colors, and overall comfort-ability. Classic cuts and lines and breathable fabrics. Stay away from prints loud prints. Base them on average sizes as well. For example: My husband wears a large hoodie in mens and I wear a medium hoodie in womens. I wear his navy blue large hoodie more often than he does as it is comfortable and gives that slouchy look. He wears my socks as he likes the fitted sock over the slouchy tube sock. Its all about common fit and common colors.