Portraits will often look better if you use a long lens. Short lenses (wide angle) will distort features and can make someone's face look objectionable. Generally "portrait lens" length is around 50mm (digital) to 85mm (full frame). Longer lenses will also create a softer more isolating background. This effect (often called shallow depth of field) eliminates distracting backgrounds and also creates a nicer effect.
Remember that your aperture can also have a huge effect on the softness of the background. Using a wide aperture will help make the background less distracting.
Each of these portraits was done with a different lens, but I adjusted my distanct to the subject to try and retain the same basic size of the person with regard to the rest of the frame. As you look at these images, pay close attention to the background and see how it changes. Also pay attention to the face and how its distortion affects the feeling of the image.