I didn't notice that "S" word in play until Dale's post.
Seance work is a field all its own and is not like any of the more traditional modes of work most folks associate with magic. We're talking about a field in which less is way more than more ever will be.
While you really should be versed in proper mentalism work (especially Cold Reading, Muscle Reading & Billet work) the real area of focus has to be learning the psychology of the Spiritualist. I'd recommend checking into the works of Bill Montana when it comes to such, and actually study the historic views when it comes to how Spiritualist Mediums worked; what was actually involved with a Seance and how little actually happened the majority of the time.
Learn all you can about Glass Moving/OUIJA styled Seance work, which includes Table Tipping & Pendulums.
WHAT NOT TO DO is run out and grab a bunch of tricks that are "spooky" and think you have a Seance. . . nor do you run thousands of yards of thread all over a room and have a half-dozen hidden helpers as one gent suggests in his horrid book "THE OTHER SIDE"
contributions & theories of a rank amateur (in other words, avoid this book!)
Study Bizarre Magick via people like Jim Magus, Larry Baukin, Brother Shadow, etc. and you will be more on "the path" of understanding when it comes to this particular niche.
Regardless, like most Seance workers, I do not encourage anyone to journey down this path until they have studied and experimented with the arena for at least a year's time. . . Oh! And don't focus on Halloween for this sort of thing unless you plan on doing the Disneyesque type Seance complete with rubber-masks, flashing lights, and smoke. As Paul will tell you, there's a huge market for solid ghost work now days (especially in most of Europe), but you need to frame everything from the perspective of the believer or those "uncertain" and leave the rest (the supposed skeptics) just as uncertain when they leave
