If you play with a higher ranked player as your duo (try for the highest possible MMR difference between you two) you can artificially inflate your MMR because you will consistently play stronger opponents.
The downside of this is that the games are going to be much tougher and the inflation only occurs if you keep winning. This will also artificially deflate your duo's MMR. The wide skill gap ma also make games frustrating as players of vastly different skills will be involved in the match.
This strategy is most useful for smurf players playing with another smurf as the duo.