There are more than 30 weapons in total of Call of Duty's arsenal of Primary, Secondary, and Accessory items, combining to hundreds of possible combinations when you count in the 3 perks. The only problem is, most of this stuff is not even available until you've leveled up! (Try past level 25 for just for the Type 100 machine gun!) This is ridiculous to the average FPSer, who wants to jump right in an start fragging with his or her favorite singleplayer weapon. But, there is a solution.
Rather than jumping right into your Team Deathmatch, War, or other more popular game modes. Take a look at a less common, but much better mode for leveling: Free for all.
Before you read on, assume you have the sufficient level to create custom classes, otherwise, start leveling with the default machine gunner until you reach that level. You will need a custom class to stand a chance in a FFA.
Free for All is one of the most difficult game modes to get the hang of. Death is imminent no matter how you play, the only thing to do is to control how long you will last. With Free For all, you want a server that doesn't change maps, and keeps a "24-7" standard on one map. My favorite is Dome, due to being a circlular map with a fair balance of hiding spots, and open spaces. You can't go wrong with a fight in there and never have to turn around and retrace steps. Once you found a good 24/7 map, it's also important to examine the perks.
Most Free for All maps are Hardcore, meaning death will happen very quickly. Some good experimental perks are Stopping Power, and Fireworks. These will help maximize your kills. You can try But one perk that is absolutely necessary is the "Toss Back" perk. Higher level players who have martyrdom (meaning they drop live grenades upon death) create great ammunition to use againts them, with this perk, the grenade will not explode in your hand, and give you the extra frags you want.
Now, let's talk about the Business end of our classes.