There are two major techniques in any debate because there are two basic possible weaknesses to any argument:
1) The conclusion is incorrectly derived from the premises;
2) The premises themselves are not factual.
The first weakness is best attacked with rhetoric (which could be described as "reasoning about reasoning"), analogies, identification of fallacies, etc. The second weakness is attacked by the presentation of evidence, although that itself is open to the first weakness because we cannot present
evidence over the internet; only references to evidence. The scientific peer-review community provides a legitimate basis to conclude that a given reference to evidence is actually itself evidence so long as the reference meets certain requirements for credibility.
I myself find it easier to attack the first weakness than the second. Others may find the reverse true for themselves. I think there's a tendancy among some to consider the second attack to be superior or more desired than the first, but both of these are legitimate, required lines of attack against creationists. Their arguments are based
both in advancing premises that are counterfactual
and in disguising faulty reasoning from what few premises they have that are not outright falsehoods.