find the appropriate tone
Sometimes when we argue ,it's easy get carried away.
Remember that your goal is to persuade and perhaps change your reader,not alienate them.
Instead of laying on insult or sarcasm, present your ideas in a moderate let-us-reason-together spirit.
Such a tone will persuade your readers that you are sincere in your attempts to argue as truthfully and fairly as possible.
If your readers do not respect you as a reasonable person, they certainly won't be swayed to your side of an issue.
Don't preach or pontificate either; no one likes or respects a writer with a superior attitude.
Write in your natural ''voice'' : don't adopt a pseudo-intellectual tone.
In short, to argue effectively you should sound logical,sincere ,and informed.