To choose the right size garter belt, measure your waist and hips using a measuring tape. Check the brand's sizing chart, as sizes may vary across different brands. Opt for a garter belt with adjustable elastic straps for a better fit. Ensure the garter belt fits comfortably on your waist and sits securely, with slightly longer straps in the back. Consider your needs and preferences before purchasing, such as whether you need everyday comfort or a retro-shaping effect.