Even if you're a fluent Spanish speaker, it's likely Mexico City will throw a few curve balls to test your language skills. The country and the city both have words that are regionally unique, not used elsewhere in Latin America.
Fortunately, there are a few resources that can help you along as you negotiate chilango (residents of Mexico City) Spanish. One of the most useful and entertaining is the book Chilangonario, which you can pick up at a number of bookstores, including Libreria Gandhi, which has multiple branches around the city. This dictionary of Mexican Spanish will help you decipher what your new wey just told you over chelas at the neighborhood cantina.