Reach the indicated rank to unlock the corresponding skin:
Gibson (Marine): Rank 2
Claw (Predator): Rank 3
Warrior Dome (Alien): Rank 4
Connor (Marine): Rank 5
Stalker (Predator): Rank 7
Ridged (Alien): Rank 10
Moss (Marine): Rank 13
Hunter (Predator): Rank 16
Praetorian (Alien): Rank 19
Johnson (Marine): Rank 22
Wolf (Predator): Rank 25
Rookie (Marine): Rank 28
Spartan (Predator): Rank 31
Nethead (Alien): Rank 34
Gibson (Marine): Rank 37
Lord (Predator): Rank 40
Van Zandt (Marine): Rank 43
Easy XP
Search for a ranked match in Multiplayer mode. When it says "One player in game, waiting for more players", quit, and go to the main menu. Then, load a Marine mission on the Normal difficulty with a lot of enemies, such as the Praetorian boss in the "Research Lab" mission. Simply kill enemies now to get easy XP. Repeat this as many times as desired.
Audio Diary locations
Search the indicated locations to find all 67 hidden Audio Diaries:
Part 1/2
Part 2/2
Finding collectibles
While playing as an Alien or Predator, activate your Focus to get collectibles to appear as flashes on the HUD.
Avoiding instant kills as the Marine
In Multiplayer mode, keep your back against walls to prevent getting killed instantly by Aliens and Predators.
Getting past ventilation shaft as the Alien
In Level 3 as the Alien, the Queen will tell you to get to the bottom of a shaft with a huge fan at the top. When you get close to it, another Xenomorph will be blown into the fan. If you use your Focus, you can see two vents on the opposite wall. You can use either of them and safely jump to it despite the power of the fan. As you continue, you will find more vents to hide in. Use them to make your way down.
Easy "Ain't Got Time To Bleed" achievement
During the first wave in Survivor mode, kill all enemies except one alien. Let the alien get close and hit you once or twice, then run away while your health regenerates. When the alien gets close, face left or right, wait until you get hit with the claw, and then run away. If the alien tries the headbite, try to avoid it because it stuns you for a while. If you let the alien slash you once, it will take away approximately a half bar of health; thus, you will have to let the alien slash you 60 times to regenerate 30 bars of health to get the "Ain't Got Time To Bleed" achievement. It is quicker to let the alien slash you twice, but is not as safe as just letting it slash you once.
Easy "Spin Doctor" achievement
At the checkpoint in the "Ruins" mission where you must activate the three species symbols switches to open the exit, activate your stealth, and bring up your Battle Disc. There will be two soldiers standing by each other. Line up it so you can hit both soldiers with the Battle Disc. Hit both soldiers to get the "Spin Doctor" achievement. If you fail to get the achievement, reload the checkpoint, and try again.
Achievements
Accomplish the indicated achievement to get the corresponding number of Gamerscore points:
Not Bad for A Human (50 points): Get all the Aliens vs Predator achievements.
Game Over, Man! (30 points): Complete all three Campaigns.
Club hopper (15 points): Survive The 'Party' at The Club.
Exit Strategy (15 points): Escape from C-Block.
You Have My Sympathies (15 points): Help Van Zandt.
Regicide (15 points): Defeat the Matriarch.
I Will Never Leave You... (15 points): Locate Tequila.
...That's A Promise (15 points): Get Tequila to surgery.
One Big Bug (15 points): Defeat the Praetorian.
Get to The Chopper! (30 points): Recover Weyland's datapad.
Come to Mama (15 points): Liberate the Matriarch.
Breaking Quarantine (15 points): Escape from the Research Lab.
Grunt Hunt (15 points): Wipe out all of the Marines in the Colony.
Under Pressure (15 points): Solve the riddle of the Ruins.
Grim Reaper (15 points): Harvest all available civilians in the Alien Campaign.
Alien vs Predator (30 points): Create a new species.
It Uses The Jungle (15 points): Find a way through Gateway.
Fallen Comrade (15 points): Find the Youngbloods in the Jungle.
Matter of Honor (15 points): Discover the Elite Predator's fate.
Eyes of The Demon (15 points): Retrieve the ancient mask.
World of Hurt (15 points): Survive trial by combat.
Breaking and Entering (15 points): Find a way into the Research Lab.
Reclaimer (15 points): Retrieve the second artifact.
Extinction Agenda (30 points): Destroy the Abomination.
Stay Frosty (15 points): Complete Marine Campaign on Hard difficulty setting.
I Admire its Purity (15 points): Complete Alien Campaign on Hard difficulty setting.
It Ain't No Man (15 points): Complete Predator Campaign on Hard difficulty setting.
I LOVE the Corps! (30 points): Complete Marine Campaign on Nightmare difficulty setting.
Magnificent, Isn't It? (30 points): Complete Alien Campaign on Nightmare difficulty setting.
One Ugly Mother (30 points): Complete Predator Campaign on Nightmare difficulty setting.
Harsh Language (15 points): Discover all 67 Audio Diaries.
Quite A Specimen (15 points): Destroy all 50 Royal Jelly Containers.
Fortune and Glory (15 points): Find all 45 Predator trophy belts.
Scatter Shot (15 points): As a team, kill 20 enemies in under 60 seconds in a Survivor match..
I Like to Keep This Handy (15 points): Kill 2 enemies with one shot with the shotgun.
Spin Doctor (15 points): Kill two enemies with one throw of the Battle Disc.
Let's Rock! (15 points): Kill 5 enemies with one burst from the smartgun.
Elite Sniper (15 points): Kill 10 enemies with head shots from the scoped rifle.
Stick Around (15 points): Kill 20 enemies with the Combi Stick.
Gunslinger (30 points): Kill 30 enemies with the pistol.
Welcome to The War (15 points): Play and complete your first Ranked Match in standard Deathmatch mode.
Killer Instinct (15 points): Win your first Ranked Match in standard Deathmatch mode.
Serial Killer (30 points): Win 10 Ranked Matches in any Deathmatch mode.
Very Tough Hombre (15 points): Kill 10 enemies in a row without dying in a Ranked Match.
Persecution Complex (15 points): Achieve Persecutor status more than once in any Ranked Match.
The Six Pack (30 points): Play with six friends in a Ranked Match.
Ain't Got Time to Bleed (15 points): Heal or regenerate 30 blocks of health in Survivor.
The Uninfected (30 points): Finish a Ranked Infestation match as the only remaining prey.
Welcome to The Party (30 points): Get 6000 XP in Ranked Matches.
Real Nasty Habit (50 points): Get 18060 XP in Ranked Matches