Lifehacker has posted a really useful introduction to portrait photography covering the following points.
- Use shallow depth of field to keep your subject in focus and your background out of focus. If you have a DSLR, certain lenses (like a 50mm or 85mm prime lens) will be more effective.
- Compose your photo well, drawing the eye to the right places and using an interesting setting for a more interesting portrait.
- Consider color regardless of whether or not the final photo will be in color.
- Make sure you have good lighting, whether you’re relying on available light or using an artificial setup.
- Keep your subjects having fun, engaged, and smiling as much as possible (unless a smile isn’t your goal.)