Note- this will only work when mw3 are hosting double weapon xp

So this is what you do,

1st set up class, best three perks to use would scavenger, quick draw, marksman.
Use specialist kill streaks, sleight of hand,steady aim and hardline.

Now once you have done that have your friend hover over your name in the lobby, be ready to keep pressing join game as fast as you can. then you search for face off 1v1.

It is probably best to play kill comfirmed, take turns, one person boost per map.
dont collect your enemies dog tag, that will end the game quicker, instead let your friend plant his tactical insertion on this cog tag, so he will keep recieveing 250 xp per death. You will receive 200xp per kill plus specialist bonus. Very quickly your guns xp will rise very fast and getting attachment challenges makes the xp go fast. if done properly you will get 140+ kill a game, you friend will get around 30,000 xp for collecting his dog tags. if your starting your gun at level 1 getting plus 130 kills plus getting challenges for attachments you will get your gold camo in 3 games of kill comfirmed.

Team death match chill out have a quickscope match.

Hope this helps