The plaintiff must have an individual claim to bring a class action claim.
Because a class action does not create any substantive rights, the plaintiff in a class action must, first and foremost, have an individual claim against the defendant. If the individual does not have a claim, then they cannot create one by trying to assert claims that other individuals may have.
The purpose of the class action device is to allow many similar claims to be handled efficiently with the same result.
A class action is a procedural device that allows an individual to represent a group of similarly situated people. The plaintiff (or class representative) in a class action argues that the wrong committed was essentially the same as to each member of the class, so that proving it with respect to the class representative will establish that the same wrong was committed as to the other class members.
Claims that turn on individual inquiries or unique facts generally will not work for a class action.
Many of the questions posed on Avvo concerning class actions demonstrate that the lawsuit would be premised on a set of facts that are unique to the individual asking the question. The question is not whether class members would have a common claim (such as each claiming that they were not promoted) but rather whether the facts underlying the claim are sufficiently similar (such as each claiming that they were not promoted because of race or because of age or or because gender). If you find yourself having to give a long narrative about the various events that occurred underlying your complaint, then it is not a likely candidate for a class action.
A class action may not be pursued without legal representation.
Finally, because a class action seeks to represent the interests of people other than the named plaintiffs, the lawsuit must be brought by a licensed attorney. Put simply, while an individual is permitted to represent them self in a lawsuit, they are not allowed to represent others (it would constitute the unauthorized practice of law), and the individual would not be an "adequate" class representative because they do not have legal training.