What you need:
2 People (including yourself)
Timing

Instructions:
Start a party with only you and your other person
One person waits at the Party Screen highlighting the hosts name
The host must then search for a 3rd Person Cage match
The second person must quickly then click on the person's name and "Join Game In Progress"

aka- You and the other person are in a 1vs1 match

Pick a spot in the map to continuously meet and each person takes turn getting a kill (prefferebly a headshot)
One person at the end will have 19 kills
The other will have the winning 20

Bonus: You verse the same person over and over and over on different maps and you just continuously upgrade your weapon attachments

Other bonuses- Great for completing challenges and leveling up