A little bit conflicted on the best way to do this basic of all tasks.
It's been suggested that - absent an actual sitemap - a good way to do this is to work your way through the universal navigation menu, copying URLs as you see them.
I've taken instead to pulling an XML map, sorting it alphabetically, and finding myself with page categories all sorted; then I assign terms. This has always made me feel more confident that I'm not missing pages. So for instance, sorting alphabetically will put all of the www.chocolate.com/# in one area, and so on.
How do others do this? I've never actually had a consensus, and I'm still an SEO toddler (just 2 years in :)