Whenever you construct a new platform for your Mother Base, you will notice that there are diamonds as well as a training area. It is deffinatly worth collecting all diamonds and whatever training areas you can do. I actually find that all of my training areas are available even AFTER I've done them multiple times. Deffinately repeat whatever training you have that is easy enough for you to do. It's a great easy way to get your GMP up early and even a steady income later in the game. As for the diamonds on new platforms, all you really need to do is interrogate your men and have them 'spit it out'. After that just put a marker on them to find the daimonds easily.

ALWAYS ALWAYS ALWAYS extract anything like vehicles or gun emplacements when you are able. Selling these are a great source of income and can add a nice bonus to your missions that you are on, or while free roaming. Keep in mind that its usually worth keeping at least 1 different type of vehicle when you start having your men go out on their own missions.

This is one of my most favorite missions to do if I need money or vehicles. While it doesnt pay out as much as some other, its relatively short and if you follow my guide, is so easy to make money on. Keep in mind that this isnt meant to complete ALL objectives in the mission and you will need certain tools to make this possible and as easy as can be.

What You Will Need
D-Horse with the Defficate command
Fulton Extraction capable of lifting vehicles
Stealth Tranq Weapon, preferably a pistol as you will lose your primary tranq later in this mission.

The Mission
First off, you will want to drop in at the zone north of Yakho Oboo @1800. Ride south until you are north of the small fork in the road. You NEED to tranq any men near this fork and extract them if they are worth it, otherwise just hide them away from anybody. I usually will C4 the power supply so the lights are out. The big thing here is to not be seen by anybody. Usually I only have to tranq 1 guard in the begining, then I head into the outpost courtyard to extract my first vehicle. Don't waste any time here as you need to return to the fork in the road then ride D-Horse north of it some until you are just ahead of the tents on the east side of the road. By this time, your second vehicle you will steal is around 200-500m away and closing in quickly. Park D-horse in the road and hide behind the crates under the tents then wait for the vehicle. It will stop to honk at D-Horse and thats when you extract. You will repeat this for every vehicle that comes through this way except the jeep that holds the prisoner.
Make D-Horse poop on the road a little further north than you have him parked. This will cause the jeep to spin out and make the driver and passenger dizzy. Take the time to tranq them both, but make sure that a vehicle from the south isnt nearby. If you have to chose, always extract the tanks and missle launcher vehicles first. Extract the prisoner and guards if you want them, extract the jeep, make sure the road is clear except for D-Horse. After a while you'll be told that a truck hauling 'more firepower' is coming. You absolutely need this if you dont already have a Rocket Launcher with guided missles. Wait for him to come to your trap area and he will stop to honk at D-Horse. Tranq him in the head, grab the missle launcher, extract truck and guard if he's worth it.
By the time you've got all the targets, you'll be told that the russians have sent out reinforcements to take you out. Ride north to where you entered the mission and take out the Gunship with your rocket launcher. Oncce its gone, wait for the tank that's coming and extract it. After this, your going to want to ride south through Yakho Oboo down Rt 8. After you pass the bridge, look for the fork on the NE side of the road. Park -Horse here and wait for the second tank. He will stop to honk, extract him. After this, ride back north, cross the bridge you passed and head south till you get to the guard post. You will need to get on the south side of the post without being seen. Park D-Horse there and wait for tank 3 to stop and honk at him. Extract him. Thats the easiest way to get through this that I've found to do this mission

Bonus Objective
One of the objectives for this missions says to extract 4 soldiers searching for the escaped prisoner. These 4 guards are between the mountains that lie between guard post 15 and 12. If you can do ALL objectives then you get more money but usually by the time I get to them they have already executed 1 prisoner, so you cannot complete the objective to save 6.

Things to Remember
This mission revolves around stealth. If you get seen or set off a combat alert, theirs a good chance that the combat vehicles can and will attack you, making this almost impossible. Do whatever it takes for you to complete this with stealth, as it also helps with your money.
One thing to remember is when you shoot down the Gunship, it will spot you, but it usually doesnt matter as its dead anyway.
Regarding the mission, as long as you are behind the vehicle you are extracting, you can run at it all you want or need in order to catch up to it. Just wait for the vehicle itself to pass you so it doesnt spot you. This is incredibly important to remember for this mission.

This mission is so fast and easy, plus you can extract a few walker gears as well as a truck. Essentially, since its so fast, it makes it worth while to repeat it over and over as much as you want/need. It's even easier when you have Quiet and her Guilty Butterfly. Have her attack the town and you have to do hardly anything other than extract Gears and soldiers you may want.