Avoiding the Kryll:
In the second chapter of the game, you'll be swarmed by enemy kryll if you so much as set foot in the dark. To avoid being attacked, stay in the light at all times. When there's no light in sight, look for propane canisters you can blow up to create some flames that'll scare off the kryll.
When reloading your weapon, watch the upper-right corner of the screen for a meter that counts down. Press the reload button a second time when the meter's moving bar matches up with the stationary bar. This will give you a super fast reload and put you back in the fight quicker than normal. However, if you mis-time the second button press your reload will take longer than normal.
Unlike most games, you can regain all of your health in Gears of War without the need for health packs. Simple stay in cover for a few seconds and watch as the bright-red gear in the center of the screen fades away. When the gear has comlpetely disappears, your health will be completely full.
Fighting the Wretches:
When fighting wretches--the small, shrieking enemies that don't use weapons--attack with melee strikes. The best melee strikes come from weapons other than your grenades and Lancer chainsaw rifle. The chainsaw attack is too slow to combat the swarming wretches, so stick to quick-hit melee punches for instant kills.
Finding Cog Tags:
There are thirty hidden Cog Tags scattered throughout the game. They're small and sometimes hard to find, but there's a a mark you can look out for that'll make finding the Cog Tags easier. Look for large, red Gear logos pasted on the walls--if you find a room with this large Gear logo, examine the room and you're sure to find a Cog Tag somewhere.
Berserker Beat Down (Then Beat Yourself Down):
To defeat the Beserker at the end of act one, simply dive to the side when she charges at you. Run through the doorway to your right and continue to the door at the end of the room and face your back to it. Get the Berserkers attention by shooting at her or revving the chainsaw then, dive away at the last moment when she charges causing her to break the door down for you.
How To Defeat General Raam:
In order to defeat Raam, you need to have grenades and a sniper rifle which is supplied in the center of the room before entering the boss arena. After entering the arena, stay behind the wall you ended the cut scene with. This is important because you need to maintain your distance from Raam. Also, it helps to command Don to "cease fire." This will make him run back towards you keeping him alive longer to distract Raam. The trick is to get Raam's swarm away from his body. In order to do this, you need to throw a grenade at Raam. If successful, the swarm will disperse giving you clear head shots using the sniper rifle. Repeat until he’s defeated. If you don't defeat Raam by the time he reaches your wall cover, move in the opposite direction he does and shoot when the swarm disperses. You will take damage from Raam’s machine gun, but you stay in the light which prevents the swarm from killing you.
When you are pitted against the Corpser in the Act 3 mines, there's a quick way to win. The Lancer's (chainsaw rifle) constant stream of fire makes it the weapon of choice here. Shoot at the belly of the Corpser, working any angle you can between its legs. If you hit the belly a few times, it will lift it's front legs and expose it's face. Immediately fire up at it's face and chin. It will shriek and move back.
Hurry, move up grab ammo and repeat. If you don't move fast enough wretches will arrive in waves and make things ten times harder. You must hit the Corpser's face three times. You'll back it up onto a platform with two destructable joints. They're lit up and on the ground. Shoot them both and the Corpser will plunge into the Imulsion liquid. If you're quick enough you can kill the corpser before any wretches arrive.
Wretches are most annoying since they swarm your soldier and kill him almost instantly on medium and hard. The best method to deal with them is with a shotgun or the alien repeater, since those weapons let you slug them without the dangerous downtime of the chainsaw. The shotgun is the best for the in-close situation, since you can forego the left trigger and hip fire the shotgun quickly to catch the wretches as they hop around. Smacking them if they get close is the only way to counter, short of using A to dodge.
The best way to defeat General Raam on Insane is to go with co-op. You have twice the smart firepower allowing one person get the Torque Bow and the other the sniper rifle. The bow carrying player should have at least ten arrows. The Torque Bow is the only weapon other than the grenades that will hurt the boss seriously when he has his Kryll shield. The explosion of the tips will also send the Kryll flying, allowing your partner to get in a nice head shot with the sniper rifle for a good one-two combo.
Cluster Kill Achievement:
To get the achievement killing three enemies at once ten times, go to the stage Act 3 - Evolution and locate the area of the Imulsion plant where the guy gets killed when he falls through the rotten wood floor. Take along at least one grenade and simply follow the dead guy down a hole (or any hole, if you step in the wrong spot). Run around the cellar until you think you have enough enemies following (meaning at least three running after you), tag one with a grenade melee attack. If you die, that's perfect, since you restart right at the checkpoint of that room and do it again. Achievement progress are independent of game progress. If not, reload the checkpoint and do it again.