I've never done one of these before, I may add more rules later.

1. You do not have to pick an alignment (i.e. good/evil). It is okay to be in-between and/or amoral.
But if you choose to be in-between, please lean more towards one side for balancing reasons.

2. Good does not have to win. Evil does not have to lose.

3. No godmodding (i.e. suddenly having a whole crowd of heavily-armed henchmen, for instance)

4. "Light" and "dark" powers do not have to go to a specific side. Whether powers are good or not should be determined by how they are used.

5. "Good" and "evil" tend to be subjective.
For instance, the Punisher is supposed to be a good guy but deals with the mob using bullets and bloodshed, while Batman is supposed to be a good guy but uses scare tactics.