Hair. Makeup. Personal freshness. Sweet breath. Good teeth. Stylish clothes. Skin. Finger nails. They all need looking after and management. You don’t just know instinctively how to do it, you have to learn. Some kids learn quicker than others, or are more interested than others, so it might LOOK as though they know it instinctively.
All this is true for both girls and boys (except perhaps the make-up bit). Where do you go to learn? Ask those relatives and friends that you think look good. They ought to be flattered and be willing to help. Read magazines. You can get professional help (but for our taste this feels pretty expensive, eg http://www.theglassslipper.co.uk ). Ask your local council about short courses – many run evening classes.