No one truly cares about the superpowers or quick reference back ground that you thought up a few days ago. People want a story, an experience to associate with your character. From that story the pieces will help create a press release. You need to dissect parts of the leading action to give hints of the climax without giving away the ending or story altogether.
One popular way is to ask the question. What if the reader found themselves in a similar predicament? What if a particular situation arose that forced the reader to make a hard decision? You have to create that bond between your main character and your audience. Show them your hero's struggle.Another common way to generate interest is to show-case the action. Its like the latest superhero movies where they pan right to where the heroes are clashing with the villains for that monumental battle. Share some of that great art. Give them a tease at what's inside.
Keep the marketing short and concise. You don't need to give a full explanation of your story up front. In fact that will deter a lot of your audience because they're going to feel like they just read your comic in a paraphrase. Just give them what's at stake, what's the conflict?
Don't go on about how Power Man X was created out of a secret government project and his powers are x, y, and z...and how he's the defender of all and so humble but powerful. I mean com'on, its his first appearance. How are your readers going to swallow all of that? People will read it and give you the all too common "Great job!" and forget about your comic by the time they go to the next article on Facebook.
Build the anticipation, Power Man X sacrificed everything for superpowers he never wanted. Now as the city is under siege by giant alien robots, Power Man X must risk his life to save the few people that matter the most to him or lose his humanity and life to the secret organization that created him. Add some mystery and drama.
Pictures are gold. Attach pictures of your comic book or action scenes. You'll get a much better response from your readers. Aim for color pictures. Even if your project is in Black and white, try your best to add color to the marketing. Use the cover or title to give it that spark.
Remember to pace yourself. Don't just bombard your audience with full-time marketing at all hours of the day or the typical ten postings on Facebook, one on every comic book related page you're on...because people usually are members to several of them just like yourself. Resist from the Twitter bomb...unleashing multiple tweets at once about your project.
This is very important when it comes to marketing your comic. If the reader doesn't establish that interest quickly they will move on to the next one.