This is really more of a mini-game than a mission; when prompted, grab the Walton around the corner and use it to catch Madd Dogg when he jumps. You dont need to adjust your position relative to the building; just hit forward or reverse and try to keep yourself so that the bed of the truck is beneath Doggs position. When he lands, drive him to the hospital and drop him off. You have an unlimited amount of time for this, so take it slow and dont hit anything. Youll need to do this mission to unlock the endgame series of missions in Los Santos, so get cracking.
After you finish up a couple of missions for Rosenthal, the C.R.A.S.H. boys will appear at a home outside of town, with another prototypical assassination mission. This ones simple enough; make it to the deserted town (which, as usual, is halfway across the map), then kill the agent and retrieve the dossier. Before you open fire, though, youll want to make sure you have a clean shot at the agent. Thus, youll want to work your way around to the north side of town and kill him first before taking out all of the cops and grabbing the dossier. You dont have to return it to Tenpenny to finish the mission; you end it right away.
Doesnt sound like Tenpenny has anything up his sleeve when he calls you for this mission, does he now? No, this is certainly all above board. Regardless, make sure you have a bunch of Uzi or SMG ammo, and be absolutely sure that you make the rendezvous with a couple hours of daylight remaining; this is a tough mission to complete at night. Youll also want to make your savegame at a point near the mission pickup, such as at the airstrip.
At its heart, though, this is another assassination mission, albeit one where you have to kill Officer Pulaski. Hell take off in what appears to be a Buffalo at the beginning, whereas all you have to work with is a dune buggy. (You can try to shoot him before he gets into the vehicle, but hes immune to gunfire, and even a rocket wont destroy the car.)
Your first priority is to exchange the buggy for a more solid vehicle. The buggy is nice for the desert, sure, but youll be on pavement for most of this little run, and the buggy cant take much damage. Luckily for you, the first road that Pulaski hits will be a big switchback; check your map and drive over the cliff to a point where youll land ahead of Pulaski. This should give you a minute to grab another car (preferably something big, like a Ranger), or, if no ones around, to line up a rocket or satchel charge on Pulaskis path.
If you do manage to get a new car, though, youll have to chase down Pulaski and ram him or drive-by his car until he jumps out. Its easier to say that than to do it, though, as hes a wily driver; try to hit him when hes on a long stretch of road. If he ducks into a town, tap him and try to get him caught up on a building; if you succeed, you can come alongside him and unload a bunch of shells into the side of the car. When you do enough damage to his vehicle, Pulaskill jump out and you can run him down for the win.