Choose the scope for the comparison. For example, you could focus your entire essay on the impacts of similar historical events, or on experiencing the local art and music scene, or on the demographics and political leanings in the two cities. These examples would lead to a more narrowed comparison, whereas a broader comparison might compare the two cities' climates, major industries, nightlife and religious culture, all within the same essay.
Outline the order in which you will present your points of comparisons, and allot one paragraph to each point of comparison. To represent each paragraph in the outline, write a topic sentence that states your overall opinion of how the two cities compare on a specific point. Here's an example: Austin and Nashville have both long been considered fertile ground for budding musicians, so they are both terrific places to see talented up-and-comers at inexpensive live music venues.
Write and develop each paragraph by building upon each topic sentence. Write a sentence or two detailing how the topic sentence is true for City A. Next, write a sentence or two detailing how the topic sentence is true for City B. For example, if your topic sentence introduces the similarities of 18th-century architectural sites in both Philadelphia and Dublin, you might develop the paragraph with a description of Philadelphia's panoptical Eastern State Penitentiary and next with a description of the Dublin's panoptical Kilmainham Gaol. Conclude each paragraph with a sentence that sums up the importance of this particular comparison.
Proofread your essay three times. Read the paper through once with fresh eyes to ensure that the information would make sense to you if you were reading the essay for the first time. Read through a second time to polish any sentences that would sound better with different words, phrases, or sentence structures. A third and final read---especially if you read it out loud---will help you catch any final misspellings or missing words.