#1. The burden of proof rests with those who posit assertions or propositions.
When someone makes a claim but is unable or unwilling to effectively buttress it with evidence or rational argument, there's no compelling reason to embrace it –– it's simply not proven. At best it might be anecdotally acknowledged or I.I.T. (Interesting If True).
#2. What can be asserted without evidence can be dismissed without evidence (Hitchens).
Recognizing the previous axiom, there's no need or reason to offer counter evidence or argument if your opponent asserts something without any evidence (or argument). Your debate opponent has merely failed to justify his position –– a failure of meeting the burden of proof.
#3. Extraordinary claims require extraordinary evidence (Sagan).
If someone claims they were abducted by aliens, taken to another galaxy and planet, and then given a tour of an advanced extraterrestrial civilization, we would expect compelling evidence for this claim. rather than just taking it on their say-so. On the other hand, a more reasonable explanation is that this individual is suffering from a mental delusion or just outright lying.
#4. Correlation is not causation.
That two things correlate does not necessarily mean one is the cause of the other, for it could be that a third yet unknown or unnoticed thing impacts the original two.
#5. The adequacy of an explanation is no guarantee it is the correct one.
An elegant explanation might be given, but its brilliance alone does not necessarily mean that it is the correct one in terms of explaining a particular event or phenomenon. Literal Biblical creationism may seem to some as an adequate explanation as the the question of biological diversity on our planet, but it's wrong –– species evolve over time.
#6. Do not multiply unnecessary entities when forming an explanation.
This is essentially Occam's Razor. Given two competing explanations, the one with the least amount of entities, variables, or assumptions tends to be true. There are cases where the correct explanation can be more complicated, but these are generally exceptions that prove the rule. In other words, don't replace one mystery with an even greater one.
#7. Keep an open mind, but not so open that your brain falls out.
Upon rejecting an explanation from a flat-earther, they might say I'm just not being open-minded to their proposition. The point here is that the evidence for a flat-earth is so overwhelmingly and demonstrably wrong, being open-minded about it is tantamount to buffoonery.
#8. If you don't know, suspending judgement is a virtue.
There's nothing at all wrong with saying "I don't know" rather than make an uninformed ad hoc explanation that's almost certainly wrong or no better than a guess or hunch.
#9. Avoid "We don't know, so therefore we do know" thinking (ad ignorantiam).
The universe is so amazingly complex and mysterious that man cannot fathom how it came to be, therefore it must have been created by a super-being. And there you have it: we don't know, there for we do know. This branches into the Kalam Argument and the Sustaining First Cause Argument, which I will not go into here. Both are fallacious and ultimately do not explain anything.
#10. Those who can make you believe absurdities, can make you commit atrocities.