The biggest tip that I can give my clients when it comes to styling their portrait session is to wear clothes that coordinate, not clothes that match exactly. For example, everyone can wear creams, whites, and beiges rather than everyone wearing a white top and jeans. Another option would be to pick two colors that complement each other (blue and orange) and then two neutrals.
When I pick out my own family’s clothing for portrait sessions, I usually start with the hardest person to dress (my picky teenager, haha). Once she has picked out an outfit that she likes, I then take the colors from that and use them in all other family member’s outfits.