After escorting Amanda about town, highlight the next mission on your HUD and follow the marker to a meetup with Jackie. In a back alley, Wei will have a serious talk with Jackie about ambition, initiative and leadership. Wei will convince Jackie to take the initiative and please Winston by pulling off a heist. That way, you can climb the ladder all the quicker. Jackie will tell you of a shipment coming in to Dog Eyes' port downtown, and the two of you will decide to pull off the heist and present the rewards to Winston.
Hop in the large van and follow the green marker down the street on the minimap on your HUD. Drive out to the docks and park at the green waypoint. You will have to step out and deal with a few bad guys at the dock. This will be the first time that you encounter Brawlers. These heavy soldiers cannot be grappled, and are marked by a X under their feet. You will have to deal with four enemies here, but luckily there are plenty of ways to eliminate the bad guys using the environment. You can stick one guy in the dumpster to the right, slam another bad guy into the electric box on the left-hand wall, and throw a third into the box all the way to the right. That just leaves the Brawler for you to deal with. Just counter his attacks and then follow up with a few quick punches before countering again, and you should be able to finish him off soon enough.
After you have defeated the first group of enemies, a second group of enemies will emerge from behind you. This one will only consist of three guys, and the Brawlers won't be with them this time. This means that you can simple grab, counter, and punch the guys into unconsciousness just like normal. One of them will even drop a crowbar for you when defeated, while another will yield a small knife. Pick up any items that the enemies drop, and use them against them to finish them all off very quickly.
After these enemies go down, a garage to the left will open up and a van will speed out carrying the cargo. Hop back into the van and give chase immediately. Follow the van, marked by a red marker on your HUD, down the alley and onto the street. When you hit the streets proper, a group of enemy cars will pop out to defend the cargo. This is where you will learn about the ramming mechanic, which allows you to more easily destroy enemy cars. Simply hit the X button and push the left stick left, right or forward to initiate a car check that has the potential to send cars flying everywhere. The more momentum you have behind your strikes, the more damage you will do to the enemy cars, so try to keep up a nice head of steam going as you speed down the street. A flock of three cars will emerge in front of you to defend the enemy van. Use your newfound ramming skills to send them all flying off of the road. Some of the cars might take more than one hit to take down. Note that it's usually best to try and send the enemies flying into oncoming traffic, walls, or other solid protrusions, as this will oftentimes finish them off in one solid hit.
Speed down the road towards the van. As you near it, another vehicle will speed out from your right. He will be pretty slow moving, and very lightweight, so simply shove him to the side and take him out. Keep speeding down the road. Three more cars will pop out and swarm in on you. Ram quickly to the left and the right to send the cars flying off of the road. Speed up to catch up with the van ahead. As the van goes to make a left turn, you can seize the car's decrease in speed to send it toppling over. Leave the van with Jackie and loot the enemy van, stashing all of the cargo in your car. Hop back in and speed off immediately. The cops know you're here now, and you'll need a nice head of speed going to escape from them.
The van is slow, and it will not be able to escape the cops easily. Your best bet, then, is not to outrun them, but to outgun them instead. Use your car check ability to check the cops against the walls of the narrow alley ahead as you speed off to safety. Follow the waypoint marker on the minimap on your HUD to reach the compound again, where the nature of your cargo will be revealed to be a little... well, boring. Still, Winston will be pleased with the shipment, so you're more or less in.
Completing this mission should give you enough experience points to level up your gang skill tree again. Jump into the character sheet menu and examine your upgrades. Choose carefully. You will be able to either up your resistance to melee attacks, or up the attack power of your own attacks. Examine where each skill tree goes, and choose a path based on your preferred play style. Do your prefer defense, or aggression? Once you've backed out of the character upgrade menus, you will have successfully completed this mission.