One of the most common arguments for why someone believes in God is the alleged existence of supernatural phenomena, such as miracle healings (as well as a big bunch of other party tricks that are often used in fundamentalist churches.)
One of the most common mistakes that skeptics do at this point is to start discussing these alleged supernatural events themselves. For example if the argument was the existence of miracle healings, eg. someone miraculously recovering from an incurable disease, the skeptic will typically start inquiring for more details on the alleged event itself, and offering alternative explanations.
This is a mistake because it's indirectly acknowledging the validity of the argument. Remember, the argument was: "miracles happen, therefore God exists." If this were a valid argument, it all would come down to the question of whether miracles do indeed happen or not. The skeptic will start arguing about the miracles themselves, rather than pointing out that the argument itself is flawed!
No discussion should proceed without this being made absolutely clear. The argument is incorrect. The alleged existence of miracles in no way proves the existence of a god. That's because even if they did happen, we don't know what causes them. Attributing them to a god is a fallacy. By not making this clear, and instead starting to argue about the miracle claims themselves, the skeptic is implicitly acknowledging that the argument is sound and valid. This is a trap that one should not fall into!
If, and only if, it has been clearly established that the existence of miracles does not prove the existence of a god, then it may be an interesting topic of discussion whether those miracles do happen or not. However, that's a completely different issue and should be discussed separately from the question of whether a god exists.
In fact this exact same principle can be applied to most other arguments for the existence of God as well. For example, it's often argued that the Bible contains fulfilled predictions or knowledge that would have been impossible for the people of that time to have known. Again: Even if that were completely true, it's still not proof of the existence of a god for the simple reason that we don't know where that information came from. Whether those alleged predictions do indeed say what it's claimed is a side-issue.
Do not fall for the trap. Kill the invalid argument from the get-go.