This is a question often asked and many times people encourage others to aproach any Lwa they want and in this post I will clarify this.
Allot of the times people want to apraoch the Lwa they want and not the Lwa they have . Some Lwa are forgiving and dont mind people trying to reach out to them allot of the times they ignore who ever is trying to call them mainly because the person has their own spirits in their court (Eskort). I have had people ask me if they can aproach certain spirits do I encourage people to aproach any spirits without a Leyson (Reading) ? no.
When it comes to certain spirits that are considered extremely hot like the Petwo spirits and some Nago as well they cannot be aproached out of the blue because you dont know how to serve them the way they are suppose to be served. Some spirits Like Met Kalfou a extremely hot and strong petwo spirit he cannot just be aproached out of the blue most of the time the Lwa do nothing but somestimes they do teach people a lesson which I try to help people prevent getting in trouble with the Lwa. Met Kalfou should be aproached when you have been introduced to him under the guidence of a Mambo or Houngan the reason why is Kalfou has no time for foolishness he is serious at time but he can also make jokes but if he walk closely to you often times the person is adviced from serving Kalfou because he will tell you when you can serve him. I speak from personal experience I have kalfou and for 2 years he was not served because I was adviced not to serve him but after 2 years he wanted to be served. remember we all have spirits in our court each reveal themselves to us when they deem us ready never try to rush your spirits because just as fast as they can come just as fast they go. Vodou is not about collecting spirits like pokemon this is often what people want to see who has the most spirits so they try to aproach other Lwa to try to get to work with them. Always ask if you can serve cetrain spirits and where they should go this is why its important to always be under the guidence of a Hounfo (House).
Give your spirits time and avoid aproaching spirits you dont have unless they come to you in dreams then consult you Houngan or Mambo.
I am often reminded by my Houngan that Vodou is not about me but about the community and helping heal people and help people.