An effective thesis statement establishes the focus of a compare-and-contrast essay by immediately relating important supporting details and information to the audience.
orienting and engaging the audience as well as setting the tone for the piece.
addressing any possible counter arguments against the piece’s main claim.
providing the writer’s viewpoint and two reasons why the argument is valid?

Be a little more specific

Prewriting: this stage of the writing process involve gathering and selecting ideas; teachers can students in several ways: creating lists, researching, brainstorming,reading to discover more about the author's style, talking, collecting memorabilia or clips from other texts, and free-writingdrafting: in this stage, students begin writing, connecting, and developing ideasrevising: this is the stage of writing that involves rewriting or "re-seeing; " emphasis is place on examining sentence structure, word choice, voice, and organization of the pieceediting: this stage involves checking for style and conventions--spelling, grammar, usage, and punctuationpublishing: the "going public" stage of writingevaluating: in this stage, the writer looks back at his/her work and self-evaluates, and the audience evaluates the effectiveness of the writingwriting activities : personal writing, workplace writing, subject writing, creative writing, persuasive writing, and scholarly writingpeer review: acting a referee; evaluating a colleague's work professionally