The first bit of description we get is that George was the leader, even after they had left the narrow trail. This certainly captures an essential part of their relationship.
We also learn that they are dressed identically. Often in the story we are told that Lennie tried to do things exactly as George did them.
George is described as small, quick, sharp, well-defined. In contrast, Lennie is described as huge, shapeless, loose. George's eyes are restless, whereas Lennie's are large and pale. All these details suggest intelligence and personality in George, as opposed to a duller wit and malleable personality in Lennie.
Lastly, we learn that George stops and wipes the sweat from his brow, whereas Lennie throws himself headlong towards the water and drinks with abandon. In life, George is cautious and thoughtful; Lennie is controlled by his impulses.
By the way, I object to kevinli123's characterization of Lennie as a slob. He has low intelligence and carries himself heavily, but there is nothing in the book that suggests he was a slob.
well, in the first chapter, when Lennie and George are by the river Lennie is described as having paw like hands. There are many things we can guess about Lennie from this. For example, it could mean he is very clumsy or it could mean he is a man of strength which later he shows both these things by firtly breaking curlys hand and secondly killing curlys wife, hope i could help
It is not a very clear image in the beginning. George is described as very strong and has defined features. Lennie, however, is a slob. This gives us an initial contact of these characters and we can relate this description better as we see their actions throughout the story.