A team that fails to rebut will always lose. Perceptive analysis of the logic behind opposing arguments is a powerful strategy. Speakers should always be ready to pounce on unsubstantiated assertions, logical fallacies and contradictions within the opposing case. After content and style, the strategy of a team's overall approach will be judged. Some of these 'technical' criteria can sink otherwise excellent teams.
Teamwork is sometimes under-used.
A two-member debate team should aim to work together so that they produce a consistent line of argument that flows from one speaker to another. Speakers should refer to their team partners by name and to what they have said or will say. Most audiences will not follow a random stream of consciousness. The efficient use of time in a speech is well rewarded. Finishing precisely on the five minute mark is always impressive.