1. Stay calm.
2. Use facts as evidence for your position.
3. Ask questions. If you can ask the right questions you can stay in control of the discussion and make your opponent scramble for answers.
4. Use logic. Show how one idea follows another.
5. Listen carefully.
6. Be prepared to concede a good point.
7. Study your opponent. Know their strengths & weaknesses.
8. Do not get personal. Attacks on your opponent’s lifestyle, integrity or honesty should be avoided. Attack the issue not the person.

Being confident is the key to a succesful explanation.