Try to avoid going to Vientiane on Mondays and Thursdays. That's the days the visa run services take people to the consulate so much busier in my experience
I got a tourist visa in Abu Dhabi. Was easy but you need bank statements and an employment letter. Dropped everything off and picked up passport with visa the next day.
However you book just be sure you have the address of at least the first place you stay. As long as you have that to put on your entry card you won't have an issue with immigration.
Avoid going to the embassy in Vientian Monday or Thursday morning to drop off your visa. That's the day the visa run companies take people there. So very busy. When I went before I flew into Vientian on monday and went to the consulate Tuesday morning and picked my visa up Wednesday afternoon.