In an effort to keep up with the latest business news coming out of Myanmar, on my last trip I picked up an extra Immigration Arrival/Departure Card in the Yangon International Airport.
Immigration procedures are straight forward but the lines are slow moving allow at least ½ hour to have your passport stamped.
You will need 2 photos if you are using Vias on Arrival. Waits of up to an hour in the VOA line are common if several flights are arriving at the same time.