Selecting Language Art's Curriculum

Homeschool parents today have a spectrum of choices when it comes to language arts curriculum.  Rainbow Resource, the super center of all homeschool supply companies, offer 515 full curriculums, and over 700 individual items to help with grammar/usage/mechanics.  Overwhelming!  Instead of offering a review of specific products or endorsing one company over another, I want to offer a few tips regarding languages arts in general: