Watchdogs is a two day job, so you'll have to work a little harder for your money here. The whole job involves transporting bags of cocaine, and Day 1 shoves you into the deep end of the action.
As the job begins, you'll find yourself inside a large truck. You first move should be tossing all the bags toward the front of this truck. Once done, train your weapon at the rear doors - as soon as they blow, the cops will be firing at you. After this brief shootout, the job can begin.
Now you must protect the cocaine. Take the bags from the truck and toss them to the platform directly in front of the truck engine. The loft up the stairs here makes a perfect spot to hold out during assaults. Get the bags up there, and hold out until your pickup arrives.
There are two spots where the pickup can arrive, but you should take the same action for both: daisy chain your bags. Work efficiently, and you can get all eight bags to your pickup in a timely fashion. You should then regroup at the loft.
Don't bother with the escape van that shows up shortly after - the driver is meant to die. Instead, hold out in the loft until your escape chopper arrives. When it does, run and gun your way to the escape point.