A Spiritist meeting is a "collective being whose qualities and properties are the result of the totality of its
members." item 331 -  [The Mediums Book, Chapt. XXIX, item 331] - Allan Kardec

Three Types of Meetings.

1 - Frivolous - participants regard spirit manifestations as an amusement, no serious results, frivolous questions
and conversations
2 - Experimental - production of physical manifestations  
a) for the curious - non-instructive
b) for the serious - study of the laws of the invisible world
3 - Instructive - research and study of Spiritism and its doctrine; instruction regarding morality.

What we want: Qualities of an Instructive Spiritist Meeting  

- a grave and concentrated mind
- a perfect community of views and sentiments
- reciprocity of kindly feelings among the members  
- abnegation of every sentiment contrary to charity  
- a general desire of the truth
- exclusion from the setting of everything of frivolity
- concentration of thought and desire in the pursuit of the common end and in the evocation of the spirits whose
presence is desired
- cooperation of the mediums, with the disinterested desire to be useful, without vanity, ambition, or any other
selfish motive

(a summary of other information from The Mediums Book Chapt. XXIX)