Demonstration: https://www.youtube.com/watch?v=UZjrnQrdGEQ

Step 1: Go Roly
Step 2: Tell your team to attack
Step 3: Get a quad kill with the help of your low level teammates
Step 4: Attack the enemy cube
Step 5: When the enemies respawn, kill as many of them as possible using the gas and health you still have
Step 6: When you die and respawn, go attack ASAP and ignore the enemy attackers, there's always 1-2 people defending in low level play anyways.
Step 7: Repeat step 2-6 and win before the enemy does

Also some tips:
Don't tell you teammates to not block the cube, they will always do it no matter what.
Don't annoy teammates to make sure they don't grief
If you get a griefer, ignore defending and try to win ASAP
Don't defend. People always defend in low level play, and carrying the offense is a lot more important than carrying the defense.