leaving and returning mexico if Mexican visa holder

Once you have a Temporary or Permanent Resident Visa by law you are to complete a FMM each time you leave Mexico. Normally, in box 8 you enter your TR or PR visa card number from the back of your visa. At the top write "temporary resident" or "permanent resident". At no time should it be checked "tourist" or you will need to start over proving financials at a consulate. Keep half of the FMM and turn it in when returning to Mexico. When entering Mexico at an airport you go through the line used for non-citizens. And please never have a color copy of your visa, driver's license or any other Mexican government issued ID as that is considered fraud with serious consequences.

you fill out the top half (larger part) on the way into Mexico and hand that part to immigration when you enter Mexico (go thru passport control). You use the small section at the bottom when you fly out of Mexico. You will need to get that stamped at the airport INM when you leave.