This is a system I've been having some fun with. Artist Tommie Kelly drew forty servitors that could be considered archetypal and released them as a deck of cards with a separate grimoire containing prayers and tips for working these spirits.
The method is quite simple; you essentially get yourself all fired up, declare yourself the master, command a service, and give a small offering, usually a candle. The ease of the system reminds me quite a bit of NAP, and I ended up finishing last night's work with the Dee Hay Thooth sign. It seemed to mesh well energetically, and the servant I called (The Devil) did not fail to keep an unpleasant individual away from me today.