There can be no game without it being populated by the Players and their respective Player Characters.

That said, there are certain base requirements that everyone is expected to follow:

• Character design must be approved by everyone – everyone has right of veto on a character that may seem over-powered or which flaunts the spirit of the game. This is a collaborative cf. a adversarial game. Conflict is helpful – open antagonism will just get you noticed, then killed.
• Every character will have a Dark Secret – this is something you never thought anyone would find out and which can be used as leverage against you. You buried it deep – just not deep enough. This information is not public (i.e. Character cf. Player) knowledge and should only be shared between the GM and the Player. Make it juicy as it will be used against you in a Court of Law.
• Every Character will have a Rogues Gallery – those groups you pissed off who wish you ill – actively or otherwise. There are to be at least five including – an individual or group which is more powerful than, as powerful as, and less powerful than you. They can be known publicly or only to yourself. But their motivations and the actions they will take when they catch up with you are generally clear.
• Every Character will have a Plot Hook – why are you here? Were you born here, grew up here or found yourself here through happenstance? What do you do for work? Do you have a family? How old are you? Are you a Joker, an Ace, a Deuce or just a Human? What is your relationship with Law Enforcement. Are you limited in some way – resources, movement, social standing, contacts, appearance. Do you have known groups you are affiliated to and why? (See my related post: The 100 Most Important Things To Know About Your Character).
• Consider Multiple Characters – if you want to keep it fresh, feel free to design more than one character. This will allow for interlocking stories and the ability to try out different combinations of powers and abilities.
• Consider being GM – it isn’t reasonable for one person to always be completely responsible for the adventure and so it is encouraged that everyone embrace the concept of a combined story background similar to the intent of the original books. That way you can take the campaign into new territory and ‘GM-fatigue’ doesn’t set in.
• Short story arcs – plot hooks will be reasonably simple to start with rather than go off on complicated tangents. Players can help by keeping things on track as much as possible and discussing plot concepts as openly as possible – this is intended to work for everyone rather than just be the GM’s ego trip.

Start with a character concept. Flesh out the powers you would like and their limitations. If you feel up to creating the game mechanics to support it – please jump right in – this is a relatively steep learning curve for most of us so we will all make mistakes to start with but that is no excuse not to start.