As others have said, employers don't value law review b/c of the skills you develop on the journal, they value it as a credential b/c they know it's very competitive, and law review members generally out performed the majority of their classmates.
As far as writing a good piece, from a 3L editor who graded some of the submissions at my school, there really aren't any secrets. I would say that generally, don't worry about making a ground-breaking point, but instead focus on your writing and bluebooking. Due to time pressure and exhaustion from exams, the writing isn't particularly good. So if you can produce a submission that is essentially error free, that reads well, and has a well substantiatd thesis (however modest), I think that will put you in a good position.