Take in some sightseeing, if time permits. Many airports offer public transportation that will take you straight to the city center. There you can see attractions, go to a museum, have a nice meal and so much more. Before leaving the airport, create a rough itinerary. Find out how long it will take to see specific attractions (or estimate, if no information is available). Factor in time for meals and travel time from place to place. Don’t forget to factor in unexpected surprises like traffic! Having a layover adventure is awesome, but missing your flight? Not so much. When you're sightseeing and having fun, it's easy to lose track of time. As a back up, set an alarm on your phone to alert you when you need to start heading back to the airport. Give yourself plenty of time to travel back and go through airport security again. A passport is required for all international travel. If you're traveling internationally, you need to have that (and any related travel documents) with you to get back into the airport. If you're not traveling internationally, you still need to show a photo ID or passport, since you'll be going through security again.  You may need a travel visa to enter/depart some countries. Research before you leave the airport! You may want to confirm the required documents with an airport attendant before leaving. If you're traveling internationally, it's best to be back about 3 hours before departure. If you're not, 2 hours is usually recommended. You will have to go through airport security again, which can be time-consuming. Be sure you're checked in 1 hour prior to your flight. Keep regulations in mind when you're buying souvenirs. Make sure anything you buy is within regulations so you can pass through security with ease. If you're unsure about a certain item, it's better to err on the side of caution and not purchase it. Depending on what time you're traveling, things may be pretty crowded when you get back. Be sure to factor this in when planning an excursion.

TL;DR in Chinese:
寻找机场附近的旅游景点。 制定并遵守时间表，以免错过航班。 在手机上设置一个闹钟。 携带有照片的证件、护照、签证和其它旅游文件。 在航班起飞前2-3小时返回机场。 过安检的时候，一定要遵守机场规则。