Dehong Mangshi Airport (LUM), with connections to Kunming, 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).
Taxis are ¥10 anywhere in the city north of the main provincial roads, and then jump quickly to ¥15-20 just outside that area. The meters aren't followed here.
If you want to go to Jiegao, look for the red taxis. They only travel between Jiegao and Ruili, and it's ¥5/per person. They only go to the other city (a 5-min ride) when full, and they need to know what cross streets/major areas you'd like to go to.
There is a bus between the two places but it only runs 4 times a day but is not convenient.
Booking cabs for longer rides is possible to get outside the city, but prices need to be negotiated.
This town is located at the China-Burmese border. There is much trade in imported goods, notably jade and fabrics. Wooden furniture (sourced from Burmese logs) are also widely available. Cheap souvenirs can also be bought from travelling Burmese merchants in the city, or by the sizeable number of other foreigners present in the city such as Pakistanis and Indians.
There is a large number of hotels in Ruili. Plan in advance for festivals such as the Water Festival in March.