Here’s what I’ve found in my search to satisfy the search terms:
I have not found anything conclusive about how the gods traveled between the worlds. The text I have at home, Gods of Asgard by Erik Evensen, the gods are depicted as merely traveling between worlds much as we would travel between states before modern transportation: horseback. Often they are seen walking as well.
As for meditation, I have not found a meditation specific to traveling to a nine world on Yggdrasil. I have, however, found some information about Norsemen and meditation as well as a meditation for connecting with Yggdrasil itself.
According to Volmarr, “The Vikings practised meditation too. Often times they sat some place outside to do this or even very commonly on a burial mound. Was common to place one’s cloak over oneself to block off the senses so that the focus was turned more inward while doing this. Since most Vikings lived in communal longhalls I doubt meditating at home would have been so good since was probably too much activity going on there. But since we tend to live in dwellings nowadays with less people living in them, it is more useful to meditate indoors as there is less to disturb us there. Of course outside meditation can be used as well when one wishes to feel the energies of an area for spiritual world purposes.” He offers the Icelandic conversion to Christianity as a staple example of Nordic mediation: Thorgeir Thorkelsson and his task of deciding the issue of Icelandic conversion to Christianity. He offers a Wikipedia article to support his point, but there is no mention of meditation in said article.
The following meditation is from Runelore:
Stand outside in a solitary place where you will not be disturbed. Face north and raise your arms to create the shape of Algiz.
“I connect to the tree of life. I offer myself to myself. I make contact with the runes in a spirit of love and harmony that I can give forward this blessing to all I meet.” Think on what you’ve just spoken and wait for an answer. When the answer is received, lower your arms in acknowledgement and reflect on the answer.