NFL website: http://www.speechanddebate.org/
Remember, it is important not to alienate your audience; those who already agree with you do not require convincing, but you are attempting to sway the opinions of people who do not share your point of view. In order to do so you need to demonstrate that you understand their point of view and can even see how some of their arguments seem sound, but then you need to gently demonstrate how your argument is even more sound. We might call this "the art of persuasion."
As a great debate coach once explained (paraphrased and undoubtedly not as powerful as the original):
You are waiting on the curb at MHS and need to get to Asheville; there are two rides available...
Car A comes flying up to the curb, slams on the brakes and stops; the driver hears the passenger door open and a second later floors the car, and hears the passenger door slam, keeping his/her (probably a his...) eyes directed in front of him/her. Driver A zooms from the parking lot, wheels screeching, and progresses onto the road, keeping the car floored whenever possible and taking the curves at the car's limit. Driver A speeds up the interstate with near reckless abandon and arrives in Asheville, at your destination, in an amazingly short time...
Car B comes up to the curb efficiently, but cautiously, and stops. Driver B sees the door open and waits for you to close the door and buckle up before proceeding efficiently onto the road; he/she takes the curves confidently, but not at the limit and soon you are on the Interstate. Driver B stays with the flow of the faster cars on the road and before long you find yourself safely at your destination, in Asheville.
Given this scenario, who "wins" (if winning is defined by who gets you there fastest)?
Answer: Driver/Car B...
Why? I thought Driver A got there faster...
Driver A heard the passenger door open, assumed you were in the seat, and sped away causing the door to slam shut... Keeping his/her eyes directed forward he/she never made sure you were in the seat... You weren't... If you want to help someone arrive at the destination, the first thing you do is make sure they are in the seat...
So what can we learn, about debate, from this?
In order to convince someone of your point of view, you must first get them in the seat... If you speed away without doing so you will not succeed in getting them to the destination. If someone has a differing opinion you need to demonstrate that you understand their point of view, and see the value in it, before trying to sway their opinion the other way. If you start off with harsh criticisms and forceful statements supporting your opinion you will alienate those who you are trying to convince before you ever get a chance to hold their attention. If they feel that you respect them and their opinion, you may succeed in changing their mind, and even if not maybe you at least shed a little light on the subject.