The best way would be to play capture the flag with unlimited time, unlimited score, and 1 life.This gives you 500 points for taking the flag and 2500 for returning it.Also you can complete challenges while sprinting such as marathon 1 and more.
Buy a good gun that suites you,then find a good camping spot or just run a montage (to me the best guns are commando,Aug,AK74u,AK47,and the Wa200
Well I leveled up by setting claymores in tight spaces and C4 on roofs in hiding spots. Just try to be sneaky and watch the back of you at all times. People could be anywhere!
straight up SD
just fight and fight to fast level up
u have to level all the way up to level 70 and then go into barracks and select prestige mode.
The fastest way to level up is to grind, which is killing mobs that are your level until you level. This is a quick way, but.... is incredibly boring. I suggest doing quests, and buying a leveling guide which will help you level as fast as possible. Zygors guide is the best on the market.
play hard
battle a guy in Leigon
Keep on defeating the Elite 4.Dont play pokemon. it means u have no life... play mw2
buy better weapons and fight alot then you will level up quickly .
train them and enter them in competions
just keep training
Easy. Give him or her an Experience Share, then battle a high level pokemon.
Search and destroy