i had the xbox 360 and had cod4. i went prestige once and hated it so i just stayed on that prestige. i got a ps3 and cod4 for it and i really want to know how to rank up fast. besides the point that there is double xp this weak
if you have a friend, you can play cage matches together to "boost" your levels up.
also if you have a few friends that will play, you can play domination and "boost", take it in turns capturing the enemy flag. this gets you a lot of experience
i don't condone using these methods because a lot of people get angry at it, but if you want to prestige up fast, this is probably the way to go.
if it is DOUBLE-XP weekend, try playing headquarters and search and destroy, you get a lot of XP on the double xp weekends