I feel it has to be done gradually. Actually the way it is happening. More and more sightings. Get MSM to show more and more evidence. Get people talking.
If more and more non believers see things with their own eyes, they will certainly start questioning their beliefs.
Warm them up and then full disclosure. Too sudden and total chaos. There a lot of good folk in the bible belt for example that need a gentle transition. I have some wonderful relatives that have been very faithful to their religion, and for them to have their world turned upside down would be very traumatic.
I wonder what percent of the population actually still believes that we are alone? It actually might be a lot lower percent than what we are told.