I can tell you what
isn't an effective posting style, yet we see it all too often here.
Most debates centre round a difference of opinion, neither one or the other is correct, for example the debate for and against foxhunting in the UK or abortion or healthcare. The object of the exercise is to make the most persuasive argument to influence an audience. That's why politicians who can debate well, do well.
This board is unique in that often we are dealing with fact eg mechanisms of mutation, atomic theory. Yes, the body of knowledge may be tweaked as new information comes to light, but in essence the fundamentals are established. In circumstances such as these, it doesn't matter how persuasive an argument is made, it doesn't change the facts.
The most ineffective style, imho, is one which employs the tactic we see all to often in the political world - rhetoric. Soundbites work in the political arena but they are just empty noise in the science arena. For example
I think of little David with his smooth little sling stone who felled the giant, Goliath. David became deadly with the sling & stone as a Shepherd in the wilderness and trusted in his skill and Jehovah enough to dare to confront the giant.
and
Having the smooth stone of Biblical truth and help of the majestic ruler and intelligent designer of the Universe, I am able to hold my own with the best of you.
Neither of these statements contains any factual information, rebuttal of contrary arguments, but contain what we all call "spin". In this environment that is about as ineffective as you can get
So I suppose that an effective posting style addresses the topic with facts and evidence, avoids spin and rhetoric and deals with what has actually been posted by opponents. It can include reducto ad absurdum and infact this is one of the most effective ways of countering an opposing argument.
But by far and away, the best posting style involves humour, an admission of error if you're wrong and total honesty.