Objective: Rescule Kazuhira Miller from captivity.
1. Pinpoint Kazuhira Miller's wherabouts.
2. Extract Kazuhira Miller.
3. Extract the commander of the Wakh Sind Barracks.
4. Complete the mission without being discovered by The Skulls.
5. Secure the rough diamonds hidden Spugmay Keep.
6. Extract the transport truck driver.
Completing all the mission tasks would be very difficult on the first playthrough of this mission. Since Snake doesn't get the Fulton recovery device until after the episode is played the first time (in Episode 3). It might be possible if you collect all the people you're required to extract at the final extraction point, but this would mean having to move them from drastically different areas of the map, and know their exact locations beforehand as well, since Snake can't interrogate enemies until he extracts a Russian interpreter in SIDE OP 01 (available after Episode 3).
In general a second playthrough is recommended to achieve the mission tasks. A set of first-playthrough recommendations is at the bottom of this page.
Here's a second-play walkthrough that achieves all Tasks:
TASK 05: Secure the diamonds hidden in Spugmay Keep.
Immediately after the cut scene ends and you have control of Snake, dismount D-Horse and head up the cliffs on the right. (video: 5:45) You may see a crack you can climb next to some Golden Crescent (in the video I'd already picked it). If you climb the crack, you'll find the hidden diamonds.
From here I captured the guards at the nearby outpost to hear Ocelot's tutorial (7:40) but you can just skip this.
TASK 01: Pinpoint Kazuhira Miller's whereabouts.
Head for Wialo Village, find a vantage-point to scout the soldier locations, and go around the village and approach from the other side. (video:10:40) I recommend approaching from the West (the left side) At this point you can extract the truck driver (Task 06) but doing so right next to the Command Outpost may attract attention of other guards.If you place a marker on him (either in the iDroid map or using your binoculars) you can track him and extract him later. (video: 12:10)
Mark the guards along the way, and head into the Command Outpost, heading up the stairs. If you don't want to make noise by opening the door, carefully position yourself to climb in through the open window without breaking the one next to it. Inside you'll find Info at the desk with the radio transmitter (destroying transmitters cuts off enemy contact with HQ, so they can't call in reinforcements, but will also potentially attract guards).
Alternatively, if you already have a Russian translator and head for Da Gwandai Khar, you could interrogate soldiers there in order to get Miller's location, and not have to make a trip to Wialo Village at all.
TASK 06: Extract the Transport Truck Driver.
After retrieving the information, the Truck driver will leave Wialo Village heading north. If you can get to your horse quickly without being spotted, you can follow him at a gallop without being noticed and catch him when he stops to honk at some sheep. If you fire a few silenced rounds from your silenced assault rifle at the truck (or blow out the wheels while it's stopped) he'll pop out and you can grab him.
Alternatively, his next stop is the Wakh Sind Barracks, where you can extract the commander to fulfill Task 03. If you catch him honking at the sheep, you can dismount D-Horse and jump in the back of the truck, and he'll take you to the Barracks without being detected. When the truck stops, you can grab him after he leaves the cab.
What I did in the video was simply track him on D-Horse to Wakh Sind and extract him after he stopped there. (video: 17:20).
TASK 03: Extract the commander of the Wakh Sind Barracks
As you head away from Da Gwandai Khar, Ocelot will call and tell you you're headed in the wrong direction. As long as you don't leave the mission area, don't worry about it.
Wakh Sind is heavily protected for a frontal assault, and is difficult to sneak in through the front door (though not impossible). It's much easier to come in from either the East or West. The East has a series of step-like rocks that can be climbed for access to the barracks themselves (video: 19:20). To the West is a crack that can be climbed to access a destroyed building on the other side of the facility. Interrogating any of the soldiers here will give you the location of the Wakh Sind Commander (video: 24:00).
It should be night at this point, so he should be in the housing shack towards the back of the North of the barracks closest to the ruined facility, and may be asleep. If not you can coax him to come searching for you by throwing an empty clip behind the building. Extracting him here may draw the attention of other soldiers, so you may wish to knock him out and move him away from the other soldiers.
TASK 01: Extract Kazuhira Miller
Miller is being held at the top of a large two-story building in the center of Da Gwandai Khar near the back. While I highly recommend doing recon to see guard locations (video: 30:30), the easiest way to get to Miller is probably to head from either the North or South, and hug the cliffs to the back of it. You'll know the house by the open metal door at the back.
Be careful, the post may have a guard inside, as well as some regularly patrolling outside. Miller is in a side-room on the top floor, (video: 36:00). Miller is too injured to extract by fulton, so you have to carry him out.
Upon retrieving Miller, you'll need to make your way towards the extraction point, but this is generally (unless you've made a lot of noise) pretty clear. Hug the cliffs and head down the hill towards the LZ (landing zone).
TASK 04: Complete the Mission without being discovered by The Skulls.
In a second playthrough, avoiding detection by The Skulls is very simply. If you change the LZ using your iDroid, you can completely avoid getting caught in the mist.(video 38:10)
If you do go to the original LZ, you can still avoid detection by The Skulls. If you are close enough to them (but still far enough to not be detected) The Skulls will twitch and slowly shamble towards you. If you wait long enough at the end of the bridge, the two Skulls at the end will move far enough on it that you can sneak around the right side, and completely avoid detection; though this takes some patience.
For the first playthrough don't skip past the cut scenes. In the second cinematic, Ocelot walks you through the operation of the iDroid and binoculars. Where Ocelelot has you look, the building with a glint coming off it (this is a rough diamond on the roof) is the command outpost of Da Wialo Village. In this building you can find Miller's location at Da Gwandai Khar.
Miller is in a large building on the top floor near the rear-center of Da Gwandai Khar, go up the back of either side and keep an eye out for enemy soldiers. Be careful, there may be a soldier inside.
After retrieving Miller, hug the cliffs near the rear of Da Gwandai Khar as you head towards the LZ (Landing Zone) for the chopper. After the mist keeps the chopper from landing, avoid The Skulls (the "mist unit") waiting at the edge of the bridge until the two at the end of it twitch their way far enough onto it that you can sneak by down below on the right.
After avoiding The Skulls (or if you get spotted by them) call D-Horse and make for the new extraction point. If you are spotted, and run (use D-Horse), the Skulls will zip in front of you as long as you remain moving on straight line. As soon as you see them starting to move to flank you, change your direction slightly and you'll throw them off for a moment. Continue to run until you get clear of the mist.
Enjoy the cut scene of Snake and Miller's somber reunion!
Mission 02: Diamond Dogs
After the cut-scene ends Ocelot will call you over to teach you how to use the Fulton Recovery System to extract soldiers and use Mother Base to do research. After the obligatory tutorial section ends, walk over to Ocelot again, and he'll run you through some more advanced CQC to fill out the other mission objectives.