Pope's "Essay on Criticism" tackles not only the problems of poor criticism but also the problems of poor writing. As he writes in the first stanza of Part I, "Tis hard to say, if greater want of skill/Appear in writing or in judging ill." In other words, he asks which is worse--writing poorly or criticizing poorly? He feels that poor criticism is worse, as a poor writer bores his or her audience, while a poor critic misleads his or her audience. He goes on to say that good writing and good critical skills are both rare, as "Both must alike from Heav'n derive their light." In other words, there's a touch of the divine in both pursuits.
Critics, he feels, can go awry by relying on too much didacticism. He says in the third stanza, "So by false learning is good sense defac'd." In other words, critics' desire to seem witty can ruin their common sense. He urges critics and writers not to try to surpass their own talents. As he says, "Be sure your self and your own reach to know,/How far your genius, taste, and learning go." In other words, if they are not wits, they shouldn't try to be too clever. Instead, he advises them to follow nature. As he writes, "Nature to all things fix'd the limits fit." He tells critics and writers that they shouldn't indulge in too much pomp but should write naturally and restrain themselves. Much of the last part of Part I is dedicated to praising the ancients, such as the Greeks, who understood the importance of restraint and following nature in creating art.
In Part II, Pope says that the main cause of people's poor judgment is pride. As he writes in the first stanza of Part II, "Pride, where wit fails, steps in to our defense,/And fills up all the mighty void of sense!" He writes that a little bit of learning can cause people's downfall in writing and in criticism.
He also writes that a critic should look over the entire work of writing and not judge it based on one part. As he writes, "survey the whole, nor seek slight faults to find." He believes that perfection in writing does not exist and that the critic can praise a piece with merits even if that piece has small faults. He also believes that it's acceptable to break Aristotle's rules of drama and that an overly narrow adherence to classical drama does not always help writers.
In addition, he takes issue with writers using too many fancy devices to cover what is truly not very good. As he writes, these types of writers "hide with ornaments their want of art." In other words, these writers cover up their poor writing with ornamentation. Others use too many words or disguise the emptiness of their writing with supposed eloquence. He also criticizes the arbitrary nature of critics, who "praise at morning what they blame at night;/But always think the last opinion right." In other words, they constantly change their minds but regard themselves as " the measure of mankind."
In Part 3, he urges critics to be humble and practice restraint: "Be silent always when you doubt your sense; /And speak, though sure, with seeming diffidence." He regards the ancients, such as Horace and Erasmus, as the greatest critics and writers because they followed sense and conveyed "The truest notions in the easiest way." He finds modern critics wanting in the sense shown by the ancients.
The "Essay on Criticism" consists of some 746 lines written in heroic couplets, i.e. iambic pentameter lines rhymed aa, bb, cc, etc. To do a line by line analysis, you may wish to use an annotated test such as the one found at University of Toronto (reference 3 below). For each line, the best strategy is to start with carefully parsing the syntax of the line, and then paraphrasing it in your own words, eliminated inverted syntax and perhaps moving the contents of subordinate clauses into separate sentences, and substituting contemporary for 18th century language, e.g.,
'Tis hard to say, if greater want of skill2Appear in writing or in judging ill; could be paraphrased as: It is hard to say if the bad poet or the bad critic appears worse. Here Pope is suggesting that since criticism no harder to write than poetry, the bad critic has no more excuses for failure than the bad poet.