It's very safe.
Crime is virtually non-existent and the chances of being hit by a car accident are very low, as the roads are virtually traffic-free.
Most visitors to North Korea limit themselves to Pyongyang, the country's most prosperous city and home to the political and scientific elite. It's a kind of show city, with many impressive buildings, monuments, and attractions.
During your visit, you'll be accompanied by two (or more) friendly guides, likely in a group with other tourists, who will explain the significance of what you're seeing and tell you a little about Kim Il-Sung and Kim Jong-Il. You can chat with the locals and enjoy a beer at a local bar or sample authentic North Korean cuisine at a restaurant.
You will likely see giant statues of these deceased rulers, and many public buildings and landmarks bear their names or were built by them.
If you go during certain times of the year, you can witness the Mass Games (or their rehearsals), or even a military parade.
If you go where you're told to go, see what you can see, photograph only what you're told to photograph, and don't do anything stupid, you'll be fine.
However, be aware that the city's friendly face is largely a facade, and attempting to peek behind the curtain is an invitation to expulsion from the country at best, and imprisonment and torture at worst.
For example, your guides are actually government spies working in pairs to spy on you and others, because the government doesn't trust them not to try to defect. All the places you'll visit are carefully selected to make a positive impression, and the locals you'll talk to are likely well-versed in what they can and cannot tell you.
Ask them about the widespread poverty in North Korea, the famines where millions of people have starved to death on the streets, or even the baseball-sized growth on the back of Kim Il-Sung's neck, and you'll see what happens when the artificial smiles on the faces of polite citizens are replaced by confusion, hostility, or fear.
Don't do anything that might make your host think you are anything other than a tourist impressed by the modern North Korean way of life and in emotional awe and gratitude towards Kim Il-Sung and Jong-Il.