A lot of the names in Oliver Twist are important – especially for the main character. Oliver’s name is given to him by the parish authorities, though, so his name isn’t actually a reflection of his real character. In fact, it’s actually in contrast to his true character. Go take a look at the "Character Analysis" section for Oliver for more on that. But the names of the minor characters are important, too: Rose Maylie, for example, is as fresh, delicate, pure, and natural as a rose, and that’s the idea her name is meant to convey. Her last name, too, connotes the freshness of springtime ("May"), and also of gladness (it rhymes with "gaily"). The same can be said of her mother, Mrs. Maylie. Mr. Bumble’s name is pretty obvious – he’s a bumbling fool. The irony slices pretty deep with him – we’re not meant to look much beyond the surface of his name, because honestly, there’s not much there. Mr. Grimwig’s name is equally superficial, because although he’s a "good guy," he’s also a fairly two-dimensional character (see the "Character Analysis" section for both Mr. Bumble and Mr. Grimwig for more about Dickens’s minor characters). Mr. Grimwig is always "grimly" stubborn and pessimistic. And "wig" is a reminder of the fact that he’s always threatening to "eat his own head," wig and all.
The way a character spends his or her free time is a pretty good indication of what kind of character he or she is. Mr. Brownlow, for example, has a huge library and is a bookworm. The first time we see him, his face is buried in a book so he doesn’t notice the Artful Dodger sidling up to pick his pocket. We’re all reading a book, and Dickens is an author, so bookworms are generally going to be good guys. The Maylies like to go on long walks in the countryside – this fits in well with what we already know about them, based on their name. Sikes and the other criminals like to binge drink – not a good habit, and therefore we suspect immediately that they are seedy characters. You get the idea.
This is a biggie in Oliver Twist – pretty much if a character looks like a bad guy, he or she is a bad guy. But there are a couple characters that aren’t as easy to judge: Oliver himself, and Nancy. But only foolish characters (Mr. Bumble, the gentleman in the white waistcoat, Mr. Fang, the officers who arrest Oliver) think that Oliver is a thief; characters whose opinions the narrator wants us to trust (Mr. Brownlow, Mrs. Bedwin, Rose Maylie, Mrs. Maylie) all take one look at his face and think, "there’s no way this kid’s a criminal! He looks so innocent!" Nancy looks like a criminal, and she is one – but later on in the novel, when she starts trying to help Oliver, her looks are often misinterpreted. When she goes to visit Rose, for example, the servants take one look at her and think, "the creature was a disgrace to her sex" (40.39). But then Rose is able to look past her physical appearance and understand her true character.
Social status isn’t always a reliable marker of whether a character is good or bad, but it is an important tool for characterization in Oliver Twist. For example, Mr. Brownlow and the Maylies are members of the middle class – they’re respectable, reasonably well-off, and seem to prefer the company of other members of the middle class. Monks, on the other hand, is also a member of the middle class, but he staunchly refuses to hang out with his social equals. He prefers "slumming" with members of the criminal class, and his rejection of his own social class in favor of the lower class is a big mark against him in the world of Oliver Twist.
Obviously important – the Dodger and Charley pick pockets; Oliver refuses to and actually runs away. Mrs. Maylie takes in orphans: clearly a good thing in the world of this novel. Nancy, as usual, is an exceptional case – her actions aren’t always easily interpretable, but that in itself is part of her characterization. She’s a complicated figure, and the readers (and other characters) don’t always know what to make of her. Is she acting for Oliver’s good, or not?
Oliver’s loyalty to his dead mother when Noah insults her is really important to Oliver’s development as a character. For all he knows, Noah could be right when he calls her "a right down bad ’un," but he still jumps to her defense. Family is obviously very important to Oliver: even though he doesn’t have one of his own (or because he doesn’t have one of his own), he’s always trying to create surrogate families – first with little Dick at the baby farm, and then with Mr. Brownlow, and then with the Maylies. Monks, on the other hand, robs his mother and runs away from her, insults his dead father, and is out to get his baby brother hanged.