CREATING A HERO If you have read many comic books, particularly Marvel, you know that the majority of superheroes gain their powers in a way that also defines the power itself. Therefore, if you want your hero to shoot lightning from it's body, have him get caught in a power plant accident. Or, you can take the easy way out and explain it scientifically - an experiment gone wrong, a developmental drug, or a side effect of a cure. Many hero's knew or were themselves scientists, and there is absolutely nothing wrong with taking that approach if you just want to get that aspect of the story out of the way. Or you can take the lazy way and simply make your character a random freak of nature or alien - whatever fits your story and power. Make sure you don't forget to give them weaknesses as well as powers - give your villain a chance to win.
A HERO'S CHOICE Heroes and villains are similar in every way except one: the initial choice of what they do with their power. A superhero usually has something tragic happen in his life to make him want to fight crime or help the innocent, or even simply declare war on a villain. Make sure your hero has some motivation to do whatever he is doing.
REAL LIFE If your hero has a dual identity, make sure that he has all the difficulties of normal day-to-day life. Give them a love life that is complicated by the fact that your hero can't reveal that there's a costume hidden beneath his clothes, or keeps missing dates and can't explain why. Make their job a difficulty too - turn the hero into a real person that people can relate to. Give him some character flaws - make him really impatient or some other little quirk to make him more interesting.
ANTAGONISTS The Villain in the story is just as important as the hero, and should have all the same characteristics: a cause for his power (if he has one), the motivation to do whatever he is doing be it greed power, or simply because he enjoys it. The difference is that a villain does not always necessitate a dual identity or second life - he can simply plot and scheme in his lair, or he can simply be hard to find. Give him the same amount of detail as you give your hero, because everyone loves a good villain. Also, if you decide to make this villain your hero's arch nemesis, make him have powers that somehow cancel out that of the hero. This not only makes it easy to have multiple engagements with the same villain and hero, but allows you to think of new ways for your hero to use his powers, using different manipulations of power to try to overcome his enemy. Using the previous example, the villain could be immune to electrical energy attacks, so the hero uses the currents to heat up a metal projectile, or make electronic devices turn on, off, or explode. This technique of "power manipulation" makes for very exciting battle sequences that never become monotonous.
CONSISTENCY AND CHARACTER DEVELOPMENT As your hero continues through the story, make sure you keep his character consistent - especially when it comes to his morals and motivation. If he ever has a change of heart, or makes a serious life decision, be sure to build up to that point very carefully. make him slowly come to realize that he needs to change, or that he's not doing what he wants. Make his decisions the way a person makes decisions - remember you want it to be as real as possible.