My father used to work with man who’s father was a doctor who escaped North Korea during the Korean War. He had to abandon his parents and go alone because he was traveling through war zones, eventually he got to safety by hiding and traveling in the forest and such. Now you can’t do this because the DMZ is in the way and the North Koreans will shoot you if you try to make a run for it, although I believe someone once defected that way.
The most common way is by crossing the river into China, but it is still difficult because Chinese authorities cooperate with North Korea, so you need to escape and get to the US embassy or a Consulate in China. Another popular method is defecting during the Olympics, but NK athletes usually have a security detail to make sure that doesn’t happen.