Since I am writing my own superhero, science fiction story with superheroes and super-villains, I figured I could help guide you through the same process. Remember that anybody is capable of having great imagination or able to come up with great ideas.
Things You Will NeedImagination, knowledge, media (movies, games, etc.), pen or pencil w/paper.
Step 1Brainstorm. This is a necessity for starting any kind of storyline. Brainstorm various ideas and write them all down. If you are going to create a super hero storyline, you are going to have to incorporate many elements such as settings, characters, plot, and so on. Your brain is the most important tool you will ever have. Knowledge is priceless. Remember that.
Step 2Create a World. Best thing to do when your writing a story is to imagine what kind of world or universe you want your story to take place in. Is it going to be a copy of our real world (that incorporates real-life people, objects, etc.) or is it going to be an entirely different set of worlds? Iron Man can be considered to be using a copy of the real world while Star Wars uses fictional settings. The world surrounding your story is very important and makes it much more interesting. It expands the reader's view on the story and makes them care about the world that the story takes place in.
Step 3Create a Conflict/Threat. In order for you world to have superheroes, there needs to be an existing conflict...otherwise what's the point of needing a superhero to clean up the world's mess? Here's a list of various kinds of conflicts you could use:
-Mutations/Biological Entities/Synthetic Entities
-Aliens with their laser guns (pew pew pew...just kidding)
-Out of control crime waves
-Your own conflict/threat?
Step 4Create the Characters. Of course no story is complete without the characters. I will create a separate guide for character creation since there is so much I can teach you about it. For now though, I want you to think about what kind of characters would fit into your world. As an example I want you to look at the picture of the four survivors from the video game Left 4 Dead. How do they fit into their zombie-apocalyptic filled world? Notice how rugged and worn out they look, both physically and mentally. How has their current predicament changed the way they operate or think?
Think of it this way...if a character comes from a rough environment, they will most likely wear rugged clothing or scavenged armor along with a tougher attitude. If the environment is cleaner then the characters are more likely to don tactical and more professional gear. Its all common sense really.
Remember that not every hero needs to be "super." Its just a typical title given to most heroic character nowadays. For example, Batman and the Punisher have no superpowers, yet they are considered superheroes.
Step 5Create a goal/mission. Now that you have a conflict on a world filled with many threats...how are your superheroes going to save it? Make sure when creating the story to make it as interesting and atmospheric as you possibly can while staying original and creative. Never be afraid or nervous to ask for criticism because other people's opinions will help improve your writing and your designs. Just make sure you ask the right people who have knowledge and good judgment.
If you ever need any kind of inspiration, I recommend watching superhero movies such Batman Begins or Iron Man. Playing video games can help give you some good ideas as well. Remember to be ambitious and always believe in yourself. Good luck!