You can start these missions at Salvatore's mansion once the S appears on your radar.
For this mission, head to Luigi's first of all. You need to follow Bob in his taxi, but make sure you don't get too close or you'll spook him. Wait until he reaches the docks along with a cut scene, after which you can take him out.
Reward: $15,000
Head for 8-Ball's garage for this mission. Once you've got and and activated the objective, 8-Ball will tell you to collect $100,000. Once you have it, return to the objective marker. At this point, you will receive a Sniper Rifle. You need to follow the marker on the radar to reach the docks. Find a good place to begin sniping by going upstairs and pitching your rifle on the roof. Shoot the guard to the bottom-left of the ramp and 8-Ball will begin to run. Shoot as many guards as you can to keep 8-Ball alive. With all the guards killed, 8-Ball will reach safety and you will complete the mission.
Reward: $100,000
Go to Luigi's club. If you try to get in the car, you receive a message warning you not to. Drive towards the objective on your radar to reach the docks. You then have to drive a boat for a while, until you reach the objective and eventually, your new hideout.
Reward: $20,000