The Best way is to get 50% EXP Bonus And The Highest Solder Barret you can wear with your rank. If This isn't possible, At least get the Adv. Back Pack, Adv. Radio/Compass And A Helmet. These give you around 40% EXP And Will significantly decrease the time you need to farm.
If You are able to get 80-100% EXP + Then You probably Only need to do 80 Kills; 0 seconds. To obtain The Maximum 1,100 EXP.
If 50% Or Less, You will need to do 150 Kills; 0 Seconds.
The way you farm is, Either get another computer on a n00b account, Or a friend,or people from the forums to Stand relatively still, While you repeatedly headshot them for EXP Until you reach your desired result.
2-3 People is best, Not too much lag, And It will go quickly. If You are trying to do a 1 vs 3+ Farming, You will need the Farmer to be The Host to begin the game, Also It is recommended that the Cows (Those who are standing still) are on Black List, As Black List Spawns near one another.