Legislation must be unique.
Certain topics have been debated ad nauseum in almost every league and region. The legalization of marijuana, the death penalty, and same-sex marriage are a few of the more over-debated topics.
Although these issues are interesting and highly contentious, most debaters have probably exhausted the supply of cogent arguments they can make about them.
Debaters should explore topics that have not been previously addressed in their league or region.
That said, old issues can be tackled in compelling and new ways. Legislation proposing universal health care has been debated over and over again, but that does not mean that a debater should not write a bill on health care; it merely means that he should try to propose a unique solution.
Exploring new topics is still advisable, but speakers can write fresh and interesting legislation on even the most debated topic areas.