You still have to go through the same exercise, regardless of whether you are working on a new site or an existing one. Yep! Although long-tail keywords will generally receive fewer searches than their shorter, simpler alternatives, they are much easier to rank for and are likely to attract a higher percentage of relevant searchers. I don't mind multiple copies of articles on the same site - as you find with WordPress categories or tags, but I wouldn't have tags and categories, for instance, and expect them to rank well on a small site with a lot of higher quality competition, and especially not targeting the same keyword phrases in a way that can cannibalise your rankings. Development of a prioritized list of targeted search terms related to your customer base and market segment.