I suggest starting from the ground.....doing a lot of groundwork and working your way up. That way you cover any basics that your horses original training may have missed, as well as create a really great bond with your horse as well as get him to trust and respect you, which is what natural horsemanship is all about.
I just bought a Green horse that was broken the traditional "cowboy" way and I am starting him over using Natural Horsemanship..... I have always followed these methods as part of my own nature, but even in asking questions and reading books (Pat Parelli and Julie Goodnight are my favorites) I'm learning even more things to make me a better horse person.... I think it is really kind of sad that sometimes people on here (and you know who you are) choose to reply rudely or belittle someone who is asking for more knowledge in the interest of making life more enjoyable for their horse.
The only stupid questions are the ones left unasked :P