You have a good general topic, so you can follow it in a lot of different directions. First, you need to decide on a thesis statement, the idea you want to explain and prove in your essay. Loneliness does play an important role in the play, but how? Who is lonely? Who is not? What causes people to feel lonely? What keeps them from feeling lonely?
Start with the characters. Curley's wife is lonely. Candy is not lonely as the play begins, but he will be very lonely after his dog is killed. George and Lennie are not lonely.
There seems to be a thesis idea in these characters. The characters in Of Mice and Men are not lonely if they have a companion to share their lives. I think you could explain and support this idea by discussing Curley's wife, Candy, and George and Lennie.
There are some enotes links below that will take you to some excellent materials over the play. The information you will find by using these enotes sources should help you with your essay. Good luck!
Of Mice and Men" essay on Loneliness is a basic part of human life.Every once in a One Becomes Lonely But while Steinbeck's Novella in 'Of Mice and Men "illustrates the loneliness of HE ranch life in the early 1930's and shows how people have driven to try and find friendship in order to escape from loneliness. Steinbeck creates a lonely and blue in the atmosphere at Many times book. He uses names and words Suche the town near the ranch I Called "Soledad", Which Means loneliness and the card game "Solitaire" Means by Which ones self. He Makes it clear That all the men on the ranch is lonely, with particular people lonelier Than Others. In the opening chapter, the idea of loneliness Introduces Steinbeck and men who work on ranches Lives temporary living, with no aim in life. Steinbeck uses the setting to Convey Ideas tissue. As they Were Walking Along the path, it is described as "a path beaten hard by boys coming down from the ranches to swim in the deep pool, and beaten hard by tramps who come wearily down from the highway in the evening to jungle-up near water "(p.18) This creates the setting and shows how men who have ever had work on the ranch temporary, isolated and lonely Lives. Also He writes "an ash-pile made by Many Fires" (p.18) This shows That Many men must have walked through this road to enter a lonely and miserable life, moving from ranch to ranch work finding Useless. I think all the people living in the ranch is lonely.This Provesi this bunk house WHERE WHERE Steinbeck describes the all the workers sleep. "There WAS Nailed Over Each bunk year with the opening forward apple box so it made two shelves for That personal belongings of the occupant of the bunk." (P38) The way Steinbeck describes the lonely bunkhouse indicates Their Lives. Also by only two shelves HAVING personal belongings for Their Lives Shows Their lonely insecure.