• I explain my editing marks in detail here.
• I explain how and why I comment the way I do here.
• How do other teachers define the letter grades? My description is in your syllabus. Here is another one by a different teacher.
• A funny look at how one teacher feels about students begging for grades. 
• The grade percentages and revision policy for your course are in your syllabus. These do vary.

Descriptions of Grades

An "A" assignment is: outstanding, exceptional, rich in content and unique in style; nuanced, interesting, lively, sophisticated, and superior to its peers.

A "B" assignment is: very good, strong; better than competent but may lack depth, uniqueness, liveliness or thoroughness present in an “A” response.

A "C" assignment: is satisfactory, acceptable, competent and meets many expectations.