Shortly after finishing your first official job for Lamar, he will give you a call and fill you in on your next Job in which you will have to hold up a store for some cash. After the phone call, pull up your cellphone and click "Jobs List." Activate the sole Job available and follow the waypoint to the nearby gas station. Once you are there, head inside and hold up the store by pointing your gun at the cashier. As he is filling up a bag with money, you can shoot at him to make him move faster. After he hands over the bag, exit the store and lose your Wanted Level.
Now open up your world map and scroll down the map legend with the D-pad until you get to the store icon. Here, you can filter through each of the 20 stores around San Andreas and set waypoints to their location. Take note that you can rob multiple stores in one go.
For the quickest method in obtaining this achievement, try to hit as many stores possible before the police manage to kill you. Also, instead of waiting for the cashier to fill the bag with money, punch him or kill him right away and press when behind the register to empty it yourself.
You may notice the store you just robbed disappears from your world map, but don't worry; it still counts so long as you collected the money inside. It disappears because the shop "closes down" after being robbed. If for whatever reason you lose track of your progress while working on this, you can tell which store has been successfully robbed by the indication of a small green check mark next to their icon on the world map.