George and Lennie are described in the opening paragraphs of the first chapter. Both men are dressed in denim pants and coats. They both are wearing black hats and carrying blanket roles (like a rolled up sleeping bag). They are similar in dress but opposite in physical appearance. George's physical description matches his mental persona. He is small, quick, and defined.
The first man was small and quick, dark of face, with restless eyes and sharp, strong features. Every part of him was defined: small, strong hands, slender arms, a thin and bony nose.
George's "restless eyes" reflect two aspects of his personality. One aspect is that George is always looking out for Lennie. George must constantly be aware of what is going on. The other thing is that George is physically and mentally restless. Being a wandering rancher, he is always on the move. But he keeps trying to save money in order to get out of this lifestyle.
Lennie's physical description matches his personality as well. He is large but undefined, like an animal:
. . . a huge man, shapeless of face, with large, pale eyes, and wide, sloping shoulders; and he walked heavily, dragging his feet a little, the way a bear drags his paws.
Similar to their personalities and mental capacities, George and Lennie's physical appearances also contrast. At the beginning of the novella, both George and Lennie are wearing denim trousers and coats with black hats. George is described as being a small person with sharp features. Steinbeck mentions the George has a dark face and restless eyes. Although he is skinny, George has strong hands. He also has a thin, bony nose and his arms are described as being slender. In contrast, Lennie is a massive individual with sloping shoulders. He is described as having a shapeless face with large, pale eyes. Lennie's body is much wider than George's, and he walks heavily, dragging his feet. Steinbeck also compares the way Lennie walks to the way a bear drags its paws. Despite being smaller and physically weaker, George protects and takes care of Lennie.