First stage would be a pretty simple trade, giving victory for both sides. North Korea agrees to stop further development on a nuclear bomb and stop missile development and testing.
North Korea gets to keep their current nuclear weapons. In return, US and South Korean military exercises are to be scaled down, massive economic aid and trade, investment and credits, and a pledge of non-invasion. Remember the US made a deal with the Soviet Union over the Cuban missile crisis which included a promise NOT to invade Cuba in the future nor assist anyone trying to do so.
Both sides will then promise for further talks towards "eventual" denuclearization. Such a first step deal would benefit all involved, the US, China, South and North Korea, as well as regional allies who could breathe a sigh of relief and prevents neighbors from seeking nukes as well.