Names in Middlemarch often tell you something about the character. Even the name of the town itself tells you something about the character of the town: it's in the middle of England, most of the residents are in the middle class, most of them are in the middle of the political spectrum. It's an average place. Dorothea's name comes from the Greek meaning "gift of the gods," while Rosamond's name comes from the Latin meaning "rose of the world." Even minor characters, like Mr. Featherstone, have names that mean something. Mr. Featherstone is a contrary, contradictory person, and his name, which juxtaposes two opposites ("feather" and "stone") reflects that. Mr. Farebrother is unswervingly "fair" to his fellow men. You get the picture…
It's not just a character's occupation that tells you something about them; it's how they feel about their job. For example, Lydgate's profession as a doctor isn't just a job, it's his calling. It's something he feels is his mission in life. Mr. Farebrother, on the other hand, is only a clergyman because his father was – it was like the family profession. But it's not his real passion. He would rather have been a biologist. Fred Vincy is saved from making a mistake in his choice of career by Mary Garth, who realizes that he isn't fit to be a clergyman and would be miserable trying. Instead, she encourages him to find a job that would be a better fit for his personality.
Dorothea chooses to wear simple clothes because her manners are simple and sincere. She doesn't need jewelry or fancy clothes to impress people. Rosamond, on the other hand, thinks about nothing but her clothes, jewels, and hairstyle – she's more concerned with the impression she'll make on people with her appearance than about the more spiritual concerns that absorb Dorothea.
We learn a lot about characters in Middlemarch based on their family life. Mr. Farebrother is a good guy because he supports his old mother, unmarried aunt, and unmarried sister, even though this puts such a strain on his income that he can't afford to get married himself. When Fred tells Mary Garth about the debt her father will have to pay, her concern is immediately for her parents and the sacrifice this will mean for them, rather than for Fred himself. Mr. Casaubon, on the other hand, doesn't get along with his only living relative, Will Ladislaw, and only supported him through school out of a sense of obligation.
You can tell a lot about a character's social status, education, and personality from the way they talk: for example, Rosamond corrects her mother's language and argues with her brother about slang in Chapter 11. She's more interested in expressing herself "properly" (i.e., according to arbitrary social standards) than she is about expressing herself with sincerity. Dorothea, on the other hand, almost always speaks without thinking about the effect of her words – her sincerity usually persuades people to her point of view.