As with anything in a localized, reconstructed tradition, the answers can come from “there and then” or “here and now.”
There and then altered states were most famously (and perhaps apocryphally) induced by gases leaking up from a volcanic vent. Alcohol was pretty popular in some corners of the world, too.
Here and now I’m aware that many of my co-religionists have mastered techniques, both old and new, to induce trance for oracular work, as well as open themselves to the gods in general. This is technically hearsay, because I have neither witnessed nor experienced it myself, although I have faith it’s really happening to others. I simply haven’t felt called to explore this myself, and rely upon those flashes of insight that I receive from time to time.
Someday when I’m not working three or four jobs I may yet learn what works for me. I had some powerful experiences in my pre-Hellenic days, specifically with Herne, and I’m more than a bit curious what doors I may open by going deep.