Need advise on this ritual

I’m thinking of doing a V.K. Jehannum but I need advise on it before I make plans to proceed: What color candle is appropriate for the Leviathan? What Incense would you advise I use? And what things could I request with this? Could I request anything or is the Leviathan dealing with specific kinds of requests? Oh, and whatever else you guys want me to know, feel free to tell me.