This is quite a hard mission, as you haven't got a single weapon to your name at the start. Beat up the first two guys that come towards you with machetes, and nick their weapon. Rush around to the left past the green tents and kill anybody over there and steal their weapons. If nobody is over there, somebody will turn up. If you have blind rage at this point, it'll make things easier, but if not, go slowly and watch out for the guys on the roof. Note that there is a health kit around the back of the tents as well.
After a car comes by, you can always get in there and use it as armour. Once you've taken out the newly spawned guys on the roofs, Pablo will try to escape via the dock. Kill the guys that have come off the boats and give Pablo chase. You're very lucky to have a Gun boat come along, which will be complete with two SAWs at the front. Simply press and anything in front of you will die. Go after Pablo and fill his boat with holes.
You can now start working on the downtown fronts.