For a spirit that can read minds the leader would quietly read a series of questions that have been prepared before the séance, written on identical paper with pens that don't show through and which have been sealed in identical envelopes.

The questions should be of a nature so that only the person who wrote it would know the answer, so try a very personal question, one that pertains specifically to your work or some other question that you think no-one else there would know the answer to. You could set it up by putting something special (preferably unusual - an anchor or fishing rod, for example) on your bedside table and then ask what it was.

The idea with the paper and envelopes is to ensure that the participants do not know when their question is being read. This should ensure that the participants cannot direct the movement of the glass (perhaps after the first few letters of "Gwythern" they might guess that this is the answer to the question "What was my grandmother's maiden name?" but that's alright). It becomes a bit like a game of Jeopardy, your answer comes up and you can then tell the rest what the question was. It is preferable that people do not all ask the same question so the leader might give the participants a topic or a theme (for example - you put something from your car into the bathroom, you ask some question about your first girlfriend and you put a pin in a map and ask the city - just don't let all the participants know what the other questions and topics are.)

For a non mind reading spirit leader would have to name the participant who proposed the question before the question is read out aloud. The person who wrote the question would remove his/her hand from the glass which will remove the possibility of that person from guiding the movement of the glass (even subconsciously).

One point to be made here is that if the spirit is not reading minds then the participation of the person who asked the question is not required - the spirit would have to obtain the answer by some other means than drawing it from the mind of the questioner in any case.

Personally, although I don't rate telepathy very highly, I don't think that a spirit, which is supposedly not a physical being, would have to rely on a physical phenomenon such as sound waves to know what question to answer. I doubt that that would be necessary for a spirit.