Dehong Mangshi Airport (LUM), with connections to [wiki=08b9a179ae67e6d81b865889bc2e9417]Kunming[/wiki], is the closest airport with direct flights. From there, there are taxis running constantly to Ruili for between ¥50-70 per person. The taxi leaves when the car is full. The trip takes about 2 hours, and the driver will drop you anywhere in Ruili you want (have an address/cross streets handy).
From the [wiki=08b9a179ae67e6d81b865889bc2e9417]Kunming[/wiki] western bus station, take the bus to Ruili. The ride takes between 14 and 20 hours, usually plan on around 16. Because they follow protocol, buses are not allowed to run overnight, which adds some time onto the journey.