Well, hello again, its xtreme's extreme Call of Duty tricks again, ready for the 3rd installment!
CTF
Capture the Flag. With the new additions, such as land mines, there are literally hundreds of new ways to protect your flag. My best suggestion is, get your team to put mines around the flag, so if anyone takes it, boom, they die. Note that if you return it you can run across them and score but you will die.
Single Flag
Single flag CTF. This is a test of pure skill. Get the flag, and rush it into the enemy base. I can suggest, since most maps have one for Single Flag, that you and a buddy hop into a motorcycle. Someone gets the flag, and flag person hops into the sidecar. The driver can drive them back safely, and that's it! Note that the motorcycle is very weak

HQ
Headquarters. One of my favorite game modes. Get to the HQ, with a Tank or Jeep if applies to the map, and establish it. Get to a good shooting point, and wait for the suckers to come!

War
War. My favorite game mode. Basically, be strong and push the enemy back. Get weapons such as the M1 Garand, Thompson, MP40, and MP44. I suggest using those rifle grenades. They come in handy!
Battle/Team Battle
Basically, Deathmatch and Team Deathmatch. I can suggest that you use Sniper Rifles, MP44's, and BAR's. Good Luck!
Well, my tips have once again been given. Good luck, kemosabi.
