It depends regarding the roleplay's genre, music of an undecipherable language helps (like german in guilty crown's bios theme to scifi scene). I would say japanese music is good for this but personally, since it is one of my two native languages, it is not as effective on me.

Though instrumental music helps too.

There's also sleeping, because dreams get very vivid if the mind is fretting on something and the rest is undisturbed. I do not advocate drugs but burning/smouldering dried basil leaves before rest at night seems to increase the chances of dreaming, basil is not a drug anyway. But then again, I'm someone who thinks I can surf the web and wikipedia things in my dreams as long as I rest near an unprotected wifi. So my words may not be entirely sane.