Timing is important; make a strong point after your opponents have made 2-3 lesser important points so as to overshadow what they have said.
Also, try and instigate them by politely questioning certain things they say (such as names of 'experts')
Keep your body language extremely calm but make each and every point you wish to make.
If your opponents are cutting what you are saying, take objection to it and tell the judge you don't appreciate their behaviour.
Body language tip: Don't point fingers and dont cross your arms.
To be honest, in the end only a proper combination of communication skills (body language, tone), knowledge, intelligence and confidence will help you win a debate . Best of luck.
A fun one to try is to stare directly into the eyes of the person you are debating against throughout the time that they are arguing their point. I can be rather unsettling if done right.