Seeds, which are collected in the fall, have a very limited viability and must not be allowed to dry out. You can plant freshly collected seeds in a gallon nursery pot and keep them moist in sand until the seeds germinate in spring. Plants grown from seed will flower in about 3 years. The only caveat going this route is that I read that the possibility exists for seeds to not be viable after going through this process.
Root cuttings, done in late fall, are another option. You take pieces of root several inches in length and place them in sand under cool conditions. By spring you should start seeing shoots.
I have also read where you can take leafy single node cuttings in June/July, treat it with a rooting hormone and place them in moist peat/perlite. It was suggested that this was a more successful option than root cuttings.
So basically, it all depends. It seems to be a mixed bag on what method is better.