Battle: Los Angeles

Complete the game on Hard Difficulty. The difficulty achievements do NOT stack. So you must play through each difficulty once.

Tips

-Do NOT rush towards the enemies. Stay far back and behind cover. Use crouch to stay low behind cover and pop out when you are not injured to shoot enemies.

-Avoid hiding behind cars because they can blow up. If you need to hide behind a car, make sure it is not on fire.

-Try to go for head shots or torso shots

-When you are injured, hide behind cover until you are fully healed. To be on the safe side, hide behind cover BEFORE your screen goes black and white with read around the screen. This means that you are near death.

-When fighting the Alien Air Units with the Rocket Launcher, there is a good strategy to kill them faster. Right as they start charging their shot, shoot your rocket launcher at them. Reload and shoot again quickly as possible. You can sometimes get 2 shots off before waiting for them to charge again which makes the process go by twice as fast

-You can make the game even easier by turning Aim Assist "On". Go to Help & Options, then Settings, then Game Settings to turn on Aim Assist. Make sure you click to accept. This will make sniping much easier too. An effective way to cover Nants when ever you need to.

Also, under "Unlockables/Mods", turn on Hollywood Mode and Double Physics. This will make enemy heads bigger and you reload 2x faster.

Note: Must have completed Easy and Normal difficulties first.

Achievement details:
Description: beat the game on Hard difficulty
Time to complete: 1-2 hours
Difficulty rating: 4/10

The above solutions do offer great tips. I personally beat the game without looking at solutions or activating cheats and would like to offer my 2 cents and combine all the tips in each solution that i believe are most relevant. Without tips I beat the entire game on easy and normal without dying the first time I ever played it and only died once on hard because of a stray rocket from an air enemy. Although I did not personally use their solutions, if I use a tip given in another solution I will give credit because of a first come first serve idea.

NOTE: My solution gives what i found to be the EASIEST way to beat the game on hard not necessarily the most fun or most entertaining.

NUMBER ONE: SNIPER RIFLE = BEAST
Use the sniper rifle from the moment you pick it up. There are plenty of ammo containers on the way in each mission so you should never even get low on ammo much less run out.

NUMBER TWO: TURN ON "AUTO AIM"
(mentioned in xThe Armory Wars' solution)
Go into game settings and turn auto aim "on". if u use the sniper rifle like I suggest each time u zoom in it will zoom right on an enemy, and with the sniper rifle it is almost always a one shot kill even on hard. Become accustomed to ducking in and out of cover while u reload/chamber ur weapon so you're not taking alot of damage and this will make things MUCH easier.

NUMBER THREE: DON'T STOP AT ONE ROCKET
(also mentioned in xThe Armory Wars' solution)
Pay close attention to the patterns the airships employ. Try to get a shot off as SOON as the ship starts to charge (stops firing machine gun and glows blue) and then as soon as you've reloaded again fire again! If you time it right you can get in two shots on it EVERY time and, if you get lucky, sometimes even THREE.

NUMBER FOUR: AIR BATTLE PREDICTABILITY
Every air battle rooftop scene is basically the same. Hide behind the concrete columns while it fires the machine gun, and, this is important, change sides WHILE the aircraft fires its missles. It seems to only aim at the side ur on when firing so switch sides when it releases its barrage to steer clear of a unlucky one shot death-by-rocket. So just to be clear, stay hidden behind a column and only move when you hear the firing sound of the rockets. Don't take your time either. I made that mistake and the one time I died on hard was during one of these transitions that I didn't take seriously. Don't worry about using up all your ammo once again because there are always ammo boxes in each of these sequences, so if you're running low find the box and make a pit stop. (rooftop areas are extremely small should be easily spied)

NUMBER FIVE: USE COMMON SENSE
Since the difficulty achievements don't stack then do the obvious; play the game on the easiest difficulty FIRST, then normal, then hard. I didn't notice an increase in NUMBER of enemies across difficulties only a increase in STRENGTH and DAMAGE RESISTANCE (although if u use the sniper rifle as suggested its 99% of the time a one shot kill even on hard as stated previously). If you play the game through twice before you play it on hard you will know where the aliens are going to spawn, you will know to aim for a gas tank or to hide behind a column and you'll be ready for the alien around the corner that scared the shit out of you on your easy runthrough lol.

NUMBER SIX: USE SPRINT SPARINGLY
(mentioned in Jayour's solution)
Unlike every other game I've ever played; in Battle:LA when you run out of sprint, you don't just go back to walking speed, u actually SLOW DOWN...ALOT. To avoid this simply use sprint in bursts. There aren't any levels where u have to cover exceptional amounts of ground any ways and since you're playing on hard it may not be a bad idea to take your time. ;)

Well, hope this may help if you're actually having trouble with this achievement. If u do as suggested and play the easier difficulties first u will also unlock:

upon campaign completion during the ending cutscene.
If you feel anything could be improved or would like to add tips of your own comment below and ill add it to the solution while giving you full credit. Good luck!

Due to this game not stacking the achievements that means for this achievement you'll need to complete the game on the hard difficulty.

The game isn't very long and shouldn't take you much longer than an hour to complete, it comprises of 3 levels none of which are overly long or tough. Rather then create a text based walkthrough for you to follow I've put some videos below for you to follow. You can use them to learn the level layouts and enemy spawn locations!

It's up to you how you choose to play, I'd suggest to hang back a little and use the sniper rifle to pick the enemies off. If you have a good aim you should be able to kill most the enemies with a single shot when aiming for the head or chest. Lastly, instead of holding the sprint button it's more efficient to tap it in short bursts and it'll make it last longer.

^{* Credit to MahaloVideoGames for the videos}