After completing the previous mission, Los Desperados, you will receive a phonecall from Sweet who will tell you to take over more gang territories around Los Santos, otherwise this mission can't be triggered.
When starting the mission get in the car with Sweet and driver to the crack fortress. Once you arrive, take the bicycle or just walk to the SWAT Tank and steal it. If you have to, kill the gangsters first and then take the SWAT. Now drive the SWAT Tank back to the crack fortress and ram its front wall to break a hole in it. The tank cannot be saved without failing the mission. You enter the building on the ground floor and must work up to floor 3. Crouch to improve your accuracy, as it is very useful. Take cover when fighting in big rooms and carefully take out all enemies since there is no time limit. Repeat this process until you reach Big Smoke. After the cutscene use your assault rifle to fight Big Smoke, if you have one, use a flamethrower and burn Smoke when getting close enough, as Smoke will not attack you and will run around the room, better still, he loses health when burning so you can easily take him out. You can also use a minigun to kill him very quickly.
After the next cutscene, Frank Tenpenny will shoot a generator, causing it to explode. Use your night vision goggles to help your way through the dark. Upon reaching a burning floor, just use the fire extinguisher to put out the flames, if you beat the firefighter side-mission, just walk through it as you're fireproof. On the PC version, crouching and aiming the camera upwards from the ground up will significantly improve visibility. The time limit is generous and it is still possible to kill all enemies without panicking or being fireproof.
When you escape the fire, Tenpenny will drive away in his firetruck with Sweet hanging off the ladder, when entering the parked Feltzer just simply do what the game says; Follow Tenpenny and make sure Sweet is safe, stay close to the firetruck and DO NOT lose Tenpenny. Do not attempt to damge the firetruck or you may injure Sweet. Be careful of traffic in this mission as Tenpenny's route never changes and he isn't programmed to crash, Tenpenny's firetruck is indestructable, so don't bother trying to destroy it. Also watch out for a train when going down the tracks. You don't actually need to follow the truck up on the Mexican-inhabited hills in Las Colinas, nor on the rail track in Willowfield. Stay on the paved road within the closest possible direct distance from Tenpenny's truck, and it will be enough not to "lose" it. Driving unusually slowly is normal while taking this approach.
Once reaching East Beach, a cop will attempt to kill Sweet by stamping on his fingers. It is important that you are very close to the truck before this happens. Driving on the opposite lane helps avoid some scripted collisions. Once you have caught Sweet, he takes the wheel and you have to shoot. Kill Tenpenny's goons and take out any cop cars or Vagos following you, keep doing this until Tenpenny finally crashes off a bridge onto Grove Street. After the final cutscene the Credits will commence. Once they are over CJ will walk out the house and the mission will be passed.