If you don't want to rush this mode I have some tips after completing it 100% (all rescues, collectibles, etc.)
Stealth is vital in most cases - do not engage enemies head on when possible as you cannot tank through this mode like normal.
You can distract enemies using

to throw a rock and make enemies look/search that area.
You can tag enemies using binoculars

and zoom with

. Useful to tag enemies before attempting to engage.
You get 4 Survival Instinct perks by performing stealth kills - each kill gives you 1 perks and you lose them if you are spotted. The perks are in order (from Wiki):
Adrenaline Perk - Allows players to move faster in crouch and auto-tags enemies within 10 meters.
Ghost Perk - Reduces the noise players make when walking, sprinting and landing. Fall damage is reduced.
Sixth Sense Perk - Automatically tags enemies about to detect the player. Also makes predators less inclined to attack the player. (Consider using bait to attract animals while this perk is active)
Predator Perk - Allows the player to tag enemies through walls using the binoculars. Extends auto-tagging to 20 meters.
Finally, silenced weapons are key to survival. Here are some guaranteed locations of silenced weapons.
Bow:First NVA camp you after you get your gear back in a open air hut on the left side.
Silenced 1911 Pistol: In the tunnels on a box below the house where you find NVA Colonel Loc
Silenced Skorpion SMG:On a table at the Con Song Temple (fills sidearm slot)
Silenced CZ57 Sniper Rifle:Best stealth weapon in the game and a one-shot kill to body except heavies. Found in the sniper tower at Fishing Village (where you rescue Yokel) after crossing the river. There is no one in the tower but this will trigger Lt Col Trang to come out and try to execute Yokel just FYI.