What are some literary devices used in Midsummer Night's Dream Act 2 Scene 1?

There are a lot of literary devices being used in this scene, but I would like to focus on the poetic aspects of the scene. Probably one of the first things that a reader or audience will notice is the strict rhyme scheme going on. Right from the start of the scene, audiences will hear the familiar ABAB rhyme scheme. Then the rhyme scheme switches to rhyming couplets. As for the rhythm, it stays mostly with the iambic foot. This means that the syllables alternate an unstressed/stressed pattern. The iambic rhythm is nothing new, but Shakespeare starts it with iambic trimeter. This is something that is characteristic of lullabies, but he builds it into the much more standard iambic pentameter. It gives the scene a really awesome sense of build and progression. Many of the lines present in this scene also contain alliteration. The following four lines are a good example.

Over hill, over dale,
 Thorough bush, thorough brier,
 Over park, over pale,
 Thorough flood, thorough fire.

The prime literary device used in this scene is exposition. Exposition is used to convey vital background information in a story. When Titania and Oberon appear, much of their dialogue is expositional. We learn that Titania and Oberon's marriage is on the rocks: she has "forsworn his bed" and he is mad she would not give him a changeling child presented to her by a human friend.
Oberon and Puck's conversation sets up the complicating factor of the play: the love potion which will cause great grief and mayhem. Oberon's expositional dialogue shares the rules of the magic flower and informs the audience of his purposes in using it.
Exposition also shares a great deal about character personality and motivation. Oberon and Titania's conflict shows they are both highly emotional, selfish, and even vain people. We learn Puck is mischievous and likes causing trouble.

This act acquaints us with the magical, fanciful world of the fairies, so Shakespeare uses poetry to convey the enchanting quality of their realm. A fairy speaks with Puck in rhyming couplets: lines end on rhyming words, such as "green" and "queen," "favors" and "savors."
Shakespeare also uses vivid imagery to conjure the world of the fairies. Imagery allows us to imagine we can see, hear, touch, smell or taste what is going on in a scene. Shakespeare describes how Titania loves the young Indian boy she has adopted. She "crowns him with flowers." This is an image because can visualize her doing this. We also learn that Titania and Oberon are fighting over the boy. Shakespeare also helps us visualize  the king and queen of the fairies formerly meeting in harmony near clear fountains or under clear skies: "By fountain clear or spangled starlight sheen." This helps us better understand how their current disharmony causes storms and crop failures. We see too that the "elves" of the kingdom "creep into acorn cups" to hide from the king and queen's anger.  We can picture an elf hiding in a an acorn cup.This image communicates how tiny these fairies are. This is important, because, obviously, real actors, not tiny beings, would play these parts on stage. 
Titania speaks in metaphor when she says to Oberon that his idea that she is seeing other men is "the forgeries of jealousy." A metaphor compares two things without using like or as. A forged signature is a false signature and forged money is fake money, so she is comparing Oberon's idea of her having affairs to a false or fake object. Oberon is speaking false words.