When search is cheap and quick, it's possible to improve search by postprocessing search results and running more queries when necessary.

I use Tantivy, and add refinements like: if the top result is objectively a low-quality one, it's usually a query with a typo finding a document with the same typo, so I run the query again with fuzzy spelling. If all the top results have the same tag (that isn't in the query), then I mix in results from another search with the most common tag excluded. If the query is a word that has multiple meanings, I can ensure that each meaning is represented in the top results.