There aren’t any hard-and-fast rules for what to wear, but I recommend to keep it simple, keep it classic and keep the intent of the image in mind when selecting portrait outfits. The images are about you, not what you’re wearing; however, whenever possible your clothing should provide some context for the image.
Are these images in celebration of major career achievement? Wear an awesome, tailored suit. Celebrating your 40th birthday? Bring a cocktail dress! Simply want to celebrate you? Wear something simple and classic. Celebrating your anniversary, but don’t want a full-blown boudoir shoot? Bring something soft and flowy that suggests romance.
If you plan to bring your family for part of your session, pick coordinating but not totally matching outfits. Solids and muted colors are always best for groups, so avoid anything patterned or very bright.
Also think about where you’ll display your images. Do you want a traditional framed portrait to hang above your formal-living room mantel? If you know you want a selection of photos to hang in your casual family room, I recommend opting for fun, relaxed clothing in colors and tones that will complement the décor of the room and not your Sunday’s best.