Here I've provided a short list of some tips unique to this article and others which are rarely known, but still important enough to mention.

Anti-Claymore:
How many of you have ran into someone just as they were laying a claymore? If someone's laying down a claymore directly in front of you, if you think fast and knife them, you'll spring past the explosion point of the claymore just as they lay it. If you chose to shoot them, odds are their claymore will blow you up after you shoot them.

Be aware of bugs in the game:
1. When the Silenced G3 is equipped, the knife usually doesn't work properly, switch to your pistol just before knifing if necessary to knife or just don't knife with it.

2. When laying down you can't crawl past the top of some steps. Try crawling sideways, often times this is a great workaround for the clipping error.

Hardcore Mode Specific Tips:
1. Ever shot a teammate by mistake before? Unfortunately, me too. The hud and mini map dissapear in hardcore. There's still a way to find out where your teammates are though. If you hit escape, you can see a larger view of the mini map showing where your teammates are and the direction they're facing.

2. In hard core mode, every sniper rifle kills in one hit. You usually shouldn't even need to consider the damage a sniper rifle does when choosing your weapon.