Tools of Characterization
You probably noticed that there's a major social divide in Athens, where people are divided into hierarchical groups: royalty (Theseus and Hippolyta), nobility (Hermia, Lysander, Demetrius, Helena, and Egeus), and commoners (the "Mechanicals" or craftsmen who perform a play at Theseus and Hippolyta's wedding). Obviously, those at the top have a lot more power than the characters at the bottom of the social ladder.
The upper-class characters are also a lot more educated, and the play suggests that this makes them better able to appreciate art and culture, unlike the "rude Mechanicals" who bumble their way through a performance of a classic story. At one point, Egeus says the craftsmen are "hard-handed men that work in Athens here. / Which never laboured in their minds til now" (5.1.76-77).
We also want to point out that the play's division of power isn't limited to Athens—even in the fairy world King Oberon and Queen Titania are elevated above regular old sprites (like Puck) and the fairies who live to serve them. To some extent, all of this is a reflection of the social hierarchy in Shakespeare's England, which also consisted of royals, nobles, and commoners.
Type of Being
The characters in the play fall into two categories: humans and fairies. As we know, fairies have supernatural powers and humans don't. Fairies can go whizzing around the globe in under an hour and humans can't. Fairies can sprinkle magic love juice in the eyes of hapless victims and humans can't. We could go on and on, but you get the idea.
The play also mentions some "ghosts" that come out at night and "wand'ring here and there, / Troop home to churchyards: damned spirits all" (3.2.402-404). Still, Oberon is quick to point out the following: "But we are sprits of another sort" (3.2.410). In other words, fairies like Oberon might like a good practical joke or two, but they're mostly harmless and, in some cases, they go out of their way to protect humans. (Remember how Oberon orders his crew to run around blessing Theseus's house in Act 5, Scene 1?)
Some, but not all, of the characters' names are significant in the play. Bottom, for example, is silly and ridiculous. His name implies that he's kind of an "ass." In case we didn't get the joke, Shakespeare literally transforms his head into that of a donkey. Bottom's name also refers to his profession. A weaver by trade, his name is another term for a piece a wood that weavers wrapped thread around.
In fact, all of the Mechanicals' names are clever plays on their professions. Peter Quince is a carpenter and his name sounds like "quoins," the wooden wedges used by men in his trade. Snug is a joiner and his name refers to the kind of "snug" joints craftsmen aimed for when they built furniture. Starveling is a tailor and his name plays on the common idea that all tailors were skinny. You get the idea, right?
It's interesting to us that Shakespeare gave his craftsmen names that align the men with their trades. It's almost as if their entire identities are wrapped up in their professions, as though the men can never be anything other than skilled laborers (no matter how hard they try to be skilled actors).
Speech and Dialogue
In the play, Shakespeare uses different speech styles to differentiate between the various types and classes of characters. The "rude Mechanicals" tend to speak in regular old prose (which is how we talk every day). The more "noble" and/or educated figures tend to speak a lot in verse (poetry). To differentiate the upper-class characters (like Theseus) from the commoners (like Bottom), Shakespeare usually has the members of the nobility speak in a style that's called "blank verse," or "unrhymed iambic pentameter." Sometimes, however, the young Athenian lovers speak "rhymed verse," especially when they're all worked up about their love lives. The fairies (Oberon, Titania, Puck, etc.) also speak in verse, but it's usually different from the humans because they tend to speak in what's called "catalectic trochaic tetrameter."
Before you get so stressed out that your head starts spinning around, you should relax—we explain all of this in "Writing Style," which is where you should go now.