The only way someone would have a clean library is if all their music had been created with the same tool and the same settings.
I have 2 main sources so it's not too bad - most of the mess comes from relying on CDDB databases when ripping, you get everything from typos to strange capitalization and the one that annoys me the most, micro-genre classification.
It still beats having to type everything in, I have had to type and submit about a dozen and that was dull enough.
The first clean up step I did was reduce it to about a dozen genres. Yes, it's hugely reductionist but I just can be bothered to think about all the sublabelling that goes on.
I also cleaned up most artist names to have the same pattern everywhere
Then i use the "rename from tag" option that my software uses, which also does directories. So I have artist/album (or more precisely "album artist"/album since i have quite a few "various artists" albums).
I'm currently going through the "various artists" album to put each song's real artist in, so i can properly find what I have by X or Y. And now and then I also drop lyrics in, I like that.
But no, my collection is still a mess - thank heavens for clever tag based search!