From what i've gathered around multiple pages, you ranking up depends on multiple variables:
A. The skill of the players youre matched up against. ie: if youre silver elite master and you do well against,say, a gold nova 3 (thats probably duoing with a silver 3, cause yes) youre probably helping your rank. Thats why people can rank up by losing, or some people rank down by winning or getting a tie game(even though tie games count as a win towards your overall ELO).
B. Your frags and mvps are also a big part of your quest to rank up. If you consistently earn, lets say 5 mvps and youre a solid 31/4/12 , youre on your way to gold nova 1.
The key to any competitive mode in any game is to always have a positive attitude, communicate, and place your goddamn crosshair at headshot level.