If a tag on a closed question is inappropriate (doesn't apply to the question), then you can remove/replace it , but please don't create a new tag like [graveyard], and keep in mind that retagging bumps the question to the top of the homepage, so only retag if it really needs it. It's okay for a closed question to be suggested as a related question. For example, questions might be closed because they are duplicates (but with different wording), in which case we'd want to keep the closed question around and even suggest it as a related question, making it easier for people to find what they need in the future.

If somebody uses terrible tags that just shouldn't exist, ask a moderator to merge the terrible tag into [tag-removed] (for example, I used this technique to remove the tag [newbie]). This has the advantage that it doesn't bump the question.

You should just tell people what they're doing wrong when they ask bad questions, and perhaps link them to one or two relevant questions. The point of speaking the same language as another person is to be able to communicate something without them having to just learn what you want from dozens of examples.

Retagging counts as editing (I don't completely agree with this, but the line has to be somewhere), and edits should move a question to the top of the home page. Questions are not always closed because they are completely wrong for MO. Closed questions can often be fixed up to be good questions. For these questions, edits should make them more visible so that the people who can vote to reopen them (3000+ rep users) can re-evaluate them.