This is simple: kill every enemy in the area and then kill all the reinforcements. Bring plenty of explosives. Oh, and find Jackson.
Objective: Eliminate all enemies
Objective: Defend against reinforcements
The first part of this mission is all about eliminating all the enemies. You can use the cameras in the parking lot and inside the building to check out all the guards, and use the environmental explosives to cause mayhem. Use the cars or cover to pick off stragglers with your weapons. Also use IEDs if you have them for taking out multiple guards.
However, keep some firepower for back up because as soon as these guards are dead a bunch of reinforcements will turn up. Use the hazards in the parking lot to take as many out as possible and make a stand in the building on the second floor for a height advantage.
Objective: Find Jackson
Now everyone is dead, let's go looking for Jackon. Go to the third floor to access the hacking point at the top of the stairs, which unlocks the door where you'll find Jackon.