Stop putting words into my mouth!
One way of making your own arguments stronger is to anticipate and respond in advance to the arguments that your opponent might make. That's all well and good, but when you misrepresent a position in order to make it appear weaker than it actually is, then refute this misrepresentation of the position, and conclude that the real position has been refuted, you've committed this friday's fallacy: a straw man fallacy.
It's memorable name vividly illustrates the nature of the misconception. Imagine a fight in which one of the combatants sets up a man of straw, attacks it, then proclaims victory. The straw man won't fight back and it's easy to destroy.
You need to focus your arguments against the actual argument your opponent makes, rather than refuting a caricatured or extreme version of it.
Here's an example of this fallacy of ambiguity during a debate on evolution:
1) "Evolution is false! How could a fish evolve into a hippopotamus!?"
2) "There would have to be billions of changes for that to occur, and
nobody has ever seen speciation anyway!"
3) "So it's silly...who has ever seen a fish evolve into a
4) "Therefore, evolution must be false!"
1) The straw man is built. Some straw man arguments end here, but let's go on.
2) The straw man is "knocked down" by any means necessary, pretending that the straw man is the real argument and not the ridiculous caricature created with deliberate ignorance and made-up facts.
3) The original position is connected with the straw man. The arguer is attempting to equate the outlandish claims of his straw man with the original position's claims. This makes the defeat of the straw man seem more victorious.
4) The opposition's argument is claimed to be refuted. Problem is, it missed the point by missing the facts.
Just the Facts, Ma'am
It's easy for the perpetrator to knock down their own straw man because they built it themselves; it's a tailor-made position for the person using it. They'll easily destroy its distorted facts soon after it is created.
This subtle tactic can actually fool those who aren't looking close enough. To counter a straw man argument, simply point out the facts. You can point out to them that they just knocked down their own caricature of the argument, not the facts that support the argument. A real counter-position to the above would cite the facts to support the position of evolution.
So instead of being lazy or ignorant, argue with facts and not cowardly accusations. Stick to the point!
In debate, a straw man can be used strategically without creating a fallacy. If the straw man is not too different from the arguments your opponent has actually made, a carefully constructed straw man might entice an unsuspecting opponent into defending a silly argument that he would not have tried to defend otherwise.
But most of the time, it just ends up being a fallacy -- especially in a small town.