This costume is for girls only!
Ok, first you need to dye your hair blonde, if not already. Then, get a pink dress with a white apron (no frills). Cut the strings off the apron then sew on front of the dress.
Get some gold paint and paint some markings (search Google img search for Zelda) on your forehead. Put Three triangles in a triangle shape on the top of your right hand (opposite of your palm).
Look out for Gannon, princess Zelda! If you want to make sure this guide is right, go to Google image search then search "Zelda".
Thanks to GlitchKnight for this idea