How might I write a paper on this topic? ''The history of English literature is the autobiography of English."
It is important to know that English is a Germanic language. The Celts invited Germanic tribes -- people from present-day Denmark and Germany -- to remove the Romans from their land, what was then Brittania. However, these tribes, most of whom were Angles and Saxons (from which we get the contemporary designation of Anglo-Saxon), decided to stay. By 450 AD, shortly after the Romans had been driven out, the Anglo-Saxons conquered England. In doing so, they also made their language dominant. The Anglo-Saxon tongue was comprised mostly of Middle High German and some Old Norse. From this, we get Old English.
The best known work of Old English literature is Beowulf. Any exploration into the history of English literature and language must begin here.
The centuries from 1100-1500 are the period of Middle English. After the Norman Conquest in 1066, England became "French." That is, the ruling class of England was comprised of French people from Normandy. A lot of new vocabulary was introduced into English, particularly that which was related to law and government, chivalry (which would become very important in Middle English romances), hunting, cooking, arts and letters, gardening and the organization of landscapes, etc. Much of the Old English pronunciation would remain, but Middle English literature is peppered with many French words and expressions.
One of the most important pieces of Middle English literature is Sir Gawain and the Green Knight. This lengthy poem is considered especially important in the canon because of its use of a "bob-and-wheel" rhyme scheme, which is composed of five lines. At the end of a stanza there is a "bob," which is an alliterative line. The bob is followed by a short, four-line wheel -- a group of couplets in an abab rhyme.
After Sir Gawain, consult Geoffrey Chaucer's Canterbury Tales. It is one of the most important works in English literature. It is different from everything that came before, as it is not about courtly life, like other Middle English literature, it is about the common people of London. Sir Thomas Malory's work Morte D'Arthur is the legend of King Arthur has been very popular since its inception. There have been literary revisions of the tale and movies.
By 1500, the English language saw changes in pronunciation that made it more akin to our modern English. Whereas in Middle English, the final "e" on a word was pronounced, that becomes no longer true. Whereas in Middle English, all consonants were pronounced separately, as in German (e.g., knight was "k-nig-ht), now sounds are fused together. This is the Elizabethan Age of literature. The most important authors are Edmund Spenser (The Faerie Queene), Christopher Marlowe (Doctor Faustus), possibly Ben Jonson (depending on whom you ask), and, of course, Shakespeare. The importance of theater in the dissemination of literature and language, particularly at this time when theater-going was an extremely popular form of entertainment, should not be underestimated.
In the seventeenth century, poetry develops as a form, particularly by John Milton (Paradise Lost) and John Donne.
By the eighteenth century, prose becomes more popular. Samuel Richardson's Pamela is considered to be the first novel, though there is much debate about this. Satire and essays also enter the canon. Jonathan Swift's fantasy novel Gulliver's Travels was very popular, but his essay "A Modest Proposal" is an important piece of political satire.
Under Samuel Johnson, literary criticism develops as an art form. This would continue in the Romantic period in the eighteenth and early nineteenth centuries in England. William Blake, Mary Wollstonecraft (author of A Vindication on the Rights of Woman, an early feminist tract), Lord Byron, Percy Bysshe Shelley, John Keats, Samuel Taylor Coleridge, and William Wordsworth are majorly important here. The latter two are connected to the development of Transcendentalist literature in the United States.
The kind of language used in English literature does not change significantly until we get to the twentieth-century. As new voices enter, they bring in their different dialects and idioms. Moreover, subject matter becomes raw and grittier. Writers not only focus on the external world, but also on people's inner lives. Profanity, racist language, and talk about sexuality -- all of which had been a part of the lexicon -- now enter print. In the twentieth century, the most important authors to consult are Virginia Woolf, James Joyce, Joseph Conrad, William Butler Yeats, and T.S. Eliot.
I have omitted American literature because you asked about specifically about English literature. Also, because the American literary canon has developed so richly in the last few centuries, it requires its own conversation. However, depending on the length of your paper and the breadth of subject matter you wish to cover, it might be a good idea to include some American writers.