If you started your teaching career in the late 90's or early 00's, then you probably encountered this book by Harry Wong. While some of the wisdom of the book is universal and still holds true, Wong was ahead of his time when he talks about instructional design. To paraphrase, he talks about seeing teachers walk out of the building looking like they're nearly dead from working so hard all day. Wong suggests that this is backwards. Students should be walking out looking dead from doing all of the work. Teachers should spend their time designing learning experiences for students that put the onus of work on them.
Similarly, Phil Schlechty in Working on the Work and in Engaging Students talks about the importance of instructional design over teacher performance. This is the essence of blended learning in that teachers need to account for class time and out of class time to design engaging learning experiences for students.
What does good instructional design look like?
For me, the best instructional design is the Understanding by Design framework created by Wiggins and McTighe. It's powerful for a number of reasons, but mostly it keeps the goal in front of the teacher. It forces teachers to confront the enduring understandings in their course, and it addresses transfer of learning from both previous knowledge and other disciplines. Additionally, it lends itself to a student-centered approach to learning. While UbD was written with the traditional classroom in mind, it is useful as a design framework for any learning experience.
iNacol has recently released a Blended Learning Teacher Competency Framework. This can be used to evaluate individual teachers, to sort of take the temperature of an entire faculty, or as a reflective tool. This is a good starting place for any school that is switching to a blended model.