Even though Superman is a guy, girls can easily dress up as superman you can make it sexy if you want or not.
Step 1: The top. You will need a blue shirt, it can be long sleeve, short sleeve, or tank top, and on the front of it you are going to paint on the Superman logo.
Step 2: The bottoms. You will need to get short red shorts. You can either just wear the shorts or you can get blue tights to wear under them.
Step 3: The cape. You will need to buy red fabric and cut it to the length that you want the cape to be. You will then sew the cape around the shoulders and back of the neck of the top.
Step 4: The boots. You can either find red knee high boots or get knee high red socks and wear some sort of shoes over them.
Step 5: The belt. Get yellow fabric and tie it around your waist.
If you want you can get a black wig to wear or just use your normal hair.