It is highly recommended that you play the game on Easy first so you do not have to worry about any other achievements on your Hard playthrough as well as the fact that you will have an idea of what to do in each level and how to deal with certain enemies etc. Below are some tips to help you get through the game.


Brightness - Make sure to turn this up as it will hugely help your visibility in dark areas of the game, as well missions set at night and rooms with no lighting etc. Don't forget you can use the flashlight by pressing UP as well.
Binoculars - Always use your binoculars with LEFT to mark enemies. This way you know their locations, and their status eg. Green, Orange, Red = Normal, Suspicious, Hostile) as well as the direction they're facing on the minimap which is especially helpful for when you're trying to sneak around.
Scavenge - Health packs, armour, weapons, grenades, ammo etc. are placed very frequently throughout the game, often hidden or in open buildings etc. Entering an outpost filled with enemies is not a good idea without any armour and only a quarter bar of health, therefore backtracking for items is essential, and a must on Harder difficulties.
Loadout - The best loadout for nearly any situation is to have a long ranged weapon, two assault rifles and an explosive weapon. Specifically, a sniper rifle, a rocket launcher, the M4 assault rifle and the AG36 assault rifle with scope. The M4 is the most common weapon in the game, therefore ammo is not never an issue with at least this weapon, but always pick up dead enemies ammo too.
Sniping - When you're sniping, crouching is must but when possible you should always go prone. This does not only make it harder for enemies to spot you but it also decreases the sway almost entirely so that you're more accurate, especially when going for headshot from a long distance.
Distance - Keeping your distance between enemies until they're dead is essential and especially the trigen enemy as they can kill you with one or two melee blows. If you find yourself in close quarters inside, then picking up a shotgun is greatly help against this enemy.