Dance and Music: Dance is a metaphor for marriage in many of Jane Austen's novels.  In the society in these novels a woman does not have many means by which to judge her suitors, and dance is one of the major ones.  It is also important it these novels to see whom is dancing with whom, and what dance they are dancing.  In Emma, Emma's major trial to see if Mr. Knightley is really interested in Jane is to observe whether he asks her to dance at the Cole's party.  Frank Churchill continues his charade of pretending to not care for Jane by telling Emma he does not want to dance with her.  Mr. Elton's snubbing of Harriet at the dance at the Crown Inn parallels his unwillingness to consider her for marriage. 

Charades and Riddles: Charades and Riddles are metaphors for the misunderstandings in the novel.  Emma tries to read people's feelings and preferences much as the characters would try to read a riddle, and most of the time she reads incorrectly.  We even see misunderstanding directly related to charades and riddles.  Emma reads Mr. Elton's riddle as directed to Harriet, when it is in fact directed to her.  When Emma, Jane and Frank Churchill play a word game, there is much misunderstanding, as Emma does not realize the depth of the relationship between Frank and Jane, and Jane is jealous of Frank's attentions to Emma. 

Letters: Letters in Emma are not only the major means of long-distance communication, but can symbolize the worth of the person.  Much attention is taken to the writing of letters, as many more people than just the intended recipient read them.  Miss Bates reads Jane's letters to all who visit her, and Frank Churchill's letters to Mrs. Weston are widely discussed.  It is decided that he writes a good letter and therefore is a fine man.  Mr. Martin's letter proposing marriage to Harriet is better than Emma had expected it to be considering his station.