The Serial Robbery mission can be started from the orange key icon at Cypress Flats/El Rancho Blvd as a civilian. Enter the checkpoint to start the mission. You will have 5 minutes to complete the mission, however, each shop you manage to rob will increase your time left.
Your objective is to rob 5 stores consecutively. Head to the first store, go to the robbery checkpoint and start robbing. Make sure there are no cops around you and choose nearby shops (Ammunation, Restaurants, General Stores, Bars, etc)
Once you manage to rob 5 stores, you will complete the mission and receive a reward.
Type /cancel at any time during the mission to cancel it. Please note that this will not remove your wanted level.