Luang Namtha is a town in Nothern Laos. It is a popular tourist destination, so expect lots of travelers and backpackers, hostels and guesthouses.
There are numerous villages that can be visited close to Luang Namtha. They are mostly along the northern road between Luang Namtha and Muang Sing. After walking outside of the city center, it is not difficult to be picked up on that route. There are no real paths for cars leading into the deeper jungle, they can only be done with an organized tour.
South/East towards Luang Prabang/Boten/Nong Khiaw
Walk to bridge (3A) that leads outside of the city and maybe a few hundred meters further to make it clear that you are going outside of the city. If cars don't stop - try the 2km sign first. It is likely to be dropped first in Natheuy, the section between the Chinese border and Luang Namtha.
North towards Muang Sing
Walk to the end of the city after the intersection 17A and 3A along the 17A. Walk a little longer, people are more likely to stop if you appear to be losst on the road. a 2km sign is very helpful there.
Places to avoid
It is very difficult to hitchhike inside of the city when trying to get out. Walking to the end of the city might be the fastest option (or taking a tuktuk).