After I responded to your other post about the D70, I realized you were the guy asking about the 85mm lens. As noted below, the 50mm is fine for everyday snap shots, or scenics, maybe even a full-length fashion shot in desperate circumstances, but for portraits of anything from people to animals, headshots or 3/4, you must have at least an 85, preferably longer (unless you specifically want "creative" features like wide noses or bug-eyes). My "normal" lens for headshots and the beach and studio glamour was a 105mm f2.5, sometimes the 180mm f2.8. As stated, it flattens the perspective and reduces the size proportion of features like the nose. The longer the lens, the less depth of field you have at a given f-stop, so you are more likely to throw the background out of focus. Using a larger f-stop (wide open) gives you even less. The ultimate is to shoot with a 300mm at f2.8, like this image below, but which I think was actually shot at f4. Note the out of focus sand in front and behind her. This combination - long lens, shallow depth of field - will make your model "pop" out of the background. Fashion shooters use it all the time on public streets for that reason.
Now I have two caveats about what I said above. First, I don't actually use my Nikkor "prime" lenses much anymore, the 105 and 180 I own aren't even in my bag because of my excellent Tamron zooms with 2.8 diaphrams. (I keep my 85mm f2 only for very low light situations). Second, all of the above mentioned focal lengths apply to my 35mm film camera, not their translation into digtial mode (like the D70 with its 1.5 magnification factor). So right now my most-used lens on digital, is my Tamron 28-105mm, which becomes a 45-150mm on the D70.
One more thing. If you're going to buy someone's used lens, make sure it is compatible with your digital camera. For example, neither my 85 or 105mm lenses are AI (auto-indexing) or AF (auto-focus) which makes them more difficult to use on newer cameras.
Andy Pearlman Studio