Google search is your friend. Literally.
Before you make a claim, google it to check if its true. Its not difficult, and it saves you the embarrasment of being corrected.
Also, take least extreme opposite position. For example, if someone says that all abortions are okay, a stupid person would take position that all abortions are wrong, but smart person would take position that some abortions are wrong. Generally, less extreme positions are easiest to defend. If opponent says "they all are", you say "some are not". If your opponent says "its always good", you say "sometimes its not good".
Argument is usually made from 2 claims and conclusion, claims supporting those two claims, and hidden premises and hidden assumptions.
The two claims are: base claim, and claim which links base claim to conclusion.
In order for argument to be true, both base claim and link claim must be true.
Example:
1. Abortion kills a human being (base claim)
2. Killing a human being is wrong (link claim)
C. Abortion is wrong
If either 1 or 2 is incorrect or unproved, argument is defeated.
However, all these claims depend on hidden premises/hidden assumptions.
What are hidden premises?
Hidden premises are unmentioned opposite premises which must be false for argument to be true, or unmentioned claims which must be true if argument is to be proved true.
What is opposite of "abortion kills a human being"?
It is a premise that sometimes, abortion actually doesnt kill a human being, example in cases where fetus would die anyway, and where mother would die without abortion. In that case, lack of abortion would kill a human being, not abortion.
"Killing a human being is wrong" claim also has it's opposite. By many people, it is considered justified to kill a human being if it saves more lives than it kills. For example, if you ask AI on if it would sacrifice 1 human to save 5, AI would answer yes. If you ask people about collateral damage in war, people would say that it is justified. So abortion, likewise, by some people can be justified in cases where it saves more lives than it kills and increases life expectancy in general.
Further, this premise depends on countless hidden assumptions: that one true morality exists, that free will exists, that people have enough knowledge to make such conclusion, that reality we know of is true reality, that human being is morally justified to exist, that killing human beings doesnt send them to a world better than this one...ect. I dont hold these positions, these are just examples.
Hidden assumptions are basically either unprovable claims which must be proved for premise to be true, or undisprovable claims which must be disproved for premise to be true.
Hidden assumptions are in theory perfect counter-arguments, because they cannot be disproved and they always make argument unproved.