Go online and set your killstreaks to one or more of the following: Care Package, Sentry Gun, or an Emergency Airdrop. Join a game and get the killstreak, then get into a good hiding spot. Throw your red smoke grenade (killstreak) somewhere where you can see it, then wait for an enemy to attempt to steal your killstreak but miserably fail as you will kill them if they try. Alternately, if you have unlocked claymores, you can throw your red smoke grenade (killstreak) and set a claymore by it. It is a great way to score a lot of points.