What makes good ideas.

Good writing is hard because finding good ideas is hard.

Good ideas are novel, credible and relevant.

Novel ideas are often unpopular ideas. Novelty is easy, but novel and credible is hard. Credible ideas come from critical independent thinkers thinking about a topic for a long time. Think critically to notice faults in existing ideas. Assess independently to propose an alternative.

As a general rule, write about unpopular ideas that you think is true.