This mission is a fairly tough one. You are required to visit a warehouse, and destroy some Chip machines. Sounds simple, however, the warehouse is full of sharp-shooting mobsters, some of which are armed with Combat Shotguns (one clip will destroy a fully armoured and full health CJ)
Before the mission, go to Ammu-nation and ensure you have full armour, and some powerful guns (lots of ammo in the AK47, or M4). Also, go to the food outlets to ensure full health also.
Climb over the fence at the side of the warehouse (near a bus stop) Ignore the container hanging from the machinery - you can use that to get on the roof, but there is no way in from there (not that i've found, anyway.)
Shoot the petrol tank on the car parked outside, to kill the mobsters inside it. Then, a cutscene will show you walking into the building. Once you get control back, run straight back outside, turn round and aim your gun. Some men will run towards you shooting pistols, kill them. After that, try to take out the people on the gangways - one of them is armed with a combat shotgun, and you don't really want him to shoot you. Watch out - there are many other people hiding inside the building. Once it's clear, start work on the labelled white machines around the edge of the room. Check the door after destroying each one, since cars with mobsters arrive. The rocket launcher, if you have it, is handy for destroying the machines. Be careful on your way out, as there are mobsters on the containers just outside, to shoot you.
After that, you are free to drive off, nobody follows you.