It's a great idea to have a 'theme' that your family can adopt for your shoot. This could be smart, formal, casual or smart casual. Then within this theme, choose a common colour to tie everyone together visually. Dark colours are slimming and a great choice. Big, busy patterns draw attention to themselves and away from you, however, stripes, spots or florals can look lovely. Sports shirts or anything with a logo are best left at home on the day of your shoot.