You have to use an approved tour agency like Koryo Tours or Korean Friendship Association. There are a few others but these two are well known. It will be an expensive task as you're sort of forced to go to China first to obtain the DPRK visa at its embassy in Beijing. From there, it's a waiting game. Some nationalities have it harder than others (American and Japanese). You have to pay a high price for the tour which includes everything you will need there (not necessarily want!). Your guide will 're-educate' you the whole way through which I hear is a unique experience. It's advisable you keep your opinions to yourself to avoid an awkward situation. Even if you know its a lie, shut it lol. Remember that your guide's future well being is in your hands so be mindful of he or she. I really want to go too but its just too costly and iffy.