Helvetica, the world's most popular typeface, will always do what it promises - convey written information that seemlessly blends into its environment. Think about it - in the American Apparel logo, it looks engaging and sexy, and on the Wal-Mart facade, it's soulless and trashy.
As Indra Kupferschmid, co-author of Helvetica Forever puts it "Helvetica is often described as the tasteless white rice among typefaces: satisfies easily, cheap and fast. But the good thing is, you can take the design into different directions with the sauce and side dishes (the typefaces you pair with Helvetica).”
Kupferschmid has written this excellent how-to for FontShop, which shares how to use Helvetica (or another neo-Grotesque) in contrast to transitional or slab-serifs.