Posed portraits are rarely the most memorable. Ironically, they can be too stiff and come off as "trying too hard" at the same time. Candid shots, on the other hand, retain some vitality -- the risk of real life. With some practice, though, you can inject some of the natural energy of candid photography into portraits.
First of all, forget about the yearbook poses. Sure, people have more and less flattering angles, but too much "chin down, head left, eyes right," will result in unnatural, awkward facial expressions. A better technique, particularly in the age of digital cameras, is to make your subject comfortable and take as many pictures as possible. You're bound to end up with a few real gems -- no contortions necessary.
If your subject is nervous (and subjects almost always are), break the ice and get them talking. It's even better to try to get them laughing. Laughter radiates warmth and will make your subject both more photogenic and more relaxed [source: Norton]. Most people are more comfortable sitting down, so consider bringing a stool along to the location. Hands can be particularly problematic, so give your subject something to hold or frame your shots in such a way that the hands are left out.
Now we'll find out why your camera lens might be the biggest obstacle between you and great portrait photos.