what makes the opening and ending of mice and men a good one?

I can only make a general comment for you. Of Mice and Men is a frame narrative. This means the beginning and of the story has similar traits to it. George and Lennie camp out at the tranquil pond before they reach the ranch. It is a peaceful place but Steinbeck foreshadows violence to come. It is fitting that the story ends here too with the killing of Lennie.