After you plane lands in Mexico, you are directed through the airport to line up to clear customs.  Have your passport and Identification (ID) as well as your tourist form (FMT) and Customs declaration form ready for the agents.  When you reach the head of the line you are confronted with what appears to be a large traffic light; Red and Green but no Amber.  Each person is required to press a large button to randomly pick which lamp lights.  If it turns Green you are allowed to pass without inspection, and you have made it into the country hassle free.  If it goes Red, you are directed to a side counter where you are questioned and your bags are checked.  You will normally still clear in a few minutes unless drugs, concealed weapons, or any items thought to be for resale are found.  Be careful what personal items you pack, as you may have to show them to custom agents.  If you have an unusual amount of luggage or oversized bags, you may be automatically flagged for inspection.  Make sure prescription drugs are in their original containers, as Mexico has a zero tolerance for drug smuggling.

Each person is only allowed to bring in goods duty free if the value is less than $3000 pesos per person, and is for their personal use while visiting.  Anything over is subject to an import tax of about 33%.  Bringing in Pets, Food and Plants into Mexico.