Well, to be perfectly honest with you I wouldn’t. Either someone is naturally drawn to this kind of thing, in which case it’ll happen regardless, or else they’re not and it could prove harmful to their psyche (at the very least) if they tried to force it, you know what I mean? Even for those with a certain predisposition toward ecstasy and trance states it can be difficult dealing with the demands this stuff make on us physically, mentally and spiritually—especially the coming down process and its aftermath.
Probably the thing that helps the most is being familiar with other methods of altering consciousness, whether those are physically, mentally, or chemically induced. Things like dance, yoga, exercise, fasting, austerities and ordeals, sex, meditation, creative expression, drugs and alcohol—all of these and numerous other things help broaden our horizons and make these spiritual states easier to accommodate. It’s better to gradually stretch something out instead of forcing your way through it all at once, and in my experience all of these and their related techniques help the process along. They aren’t a substitute for spiritual possession and trance, but they can teach you what it’s like, how to ride it out, so that you’re better prepared for the actual experience when it happens.