Mnemonic pegging works! All you need to do is think of 10 important things you need to remember about the novel and then peg them to visual imagery by inventing a story, if necessary.
Here's mine:
1 is a lighthouse or candle. No need to invent a story. It stands for the theme of solitude and loneliness.
2 looks like a swan, but again no story is necessary. 2 stands for the companionship between the men, especially George and Lennie.
3 looks like a snake. This reminds me of the Biblical story involving Eve and the snake in The Garden of Eden. It warns us of the danger of temptation, which Curley's wife represents.
4 looks like a sailing ship. To me that is the American Dream of material wealth, but the voyage to get there is dangerous on a rough sea.
5 is the hook. Lennie has the physical strength to hang other characters on it, but lacks the mental capacity to know when to stop himself from killing accidentally.
6 is a golf club. If we hit the ball into the distance, Candy's old dog will hobble after it.
7 is a boomerang, representing Lennie's innocence coming back to haunt him.
8 is a pair of spectacles. Even wearing them, many can't see past the colour of Crooks's skin.
9 is a balloon. It represents the 'pie in the sky' dream of George, Lenny and Candy to have their own farm. Ultimately, it's all just hot air.
10 is a bat and ball. Curley gets battered but he's more of a winner than Lennie, who's shot.
I hope that helps you ahead of any exams that you might have coming up.