A superhero's abilities are often his defining features and so it is important to come up with something relatively unique. Once you come up with the abilities you can build the world and character's story around them. Abilities are most often superhuman. Most superheroes have a way to travel quickly, whether it's by flying, running fast or driving a fast vehicle. Most superheros also have abilities that increase their fighting techniques, such as super strength, agility or invisibility.
After you have come up with your superhero's abilities it is important to think of the elements of your superhero's past, or, what drives him to fight evil. Many superheroes have tragic pasts, such as losing a family member or friend to an evil force or having a near-death experience. Often the past can be linked with some of the superhero's abilities. For example, Spider-Man was bitten by a radioactive spider, which gave him several spider-like traits.
When creating a superhero, it is just as important to develop the world he lives in as it is to develop his character. In order to build an environment for your superhero you will first want to decide whether you want him to live on Earth or in an imaginary world. Earth is a choice for individuals who want to play off of known elements, and the Earth you create can be ficticious. You can choose an Earth of the past, present or future, depending on what you want your characters and their surroundings to look like. An alien planet is a choice for those who would like to build from the ground up. You can come up with history of that world, plants and animals and culture.
The ethos of your character is very important to decide before you begin your comic book or novel. While superheroes, opposed to supervillians, are good, you still have plenty of personality elements to think about. While your superhero might be fighting for the good of the world, he may have vices, such as greed, obsession or potential to seek pleasure that draw him away from the side of justice. Your superhero could also have the characteristic of fighting on his own side for what he believes to be justice, giving him a sort of outlaw appeal (like Marvel's character Punisher).