Get to know your subject;
Chat and connect with your subject prior to your photo session. Make them feel relaxed and at ease during the session by offering some simple direction, this can go a long way!
Make your subject the focus;
Portrait photography works best using a wide aperture, ideally use a range between 2.8 - 5.6. Capturing a shallow depth of field will make your background blur, allowing your subject to really stand out. The easiest way to achieve this is to set your camera to aperture priority mode, this will control the depth of field and set the shutter speed for the correct exposure.
Choosing the right lens:
A lens which allows a wide aperture is what you need. If you choose a 1.4 - 2.8 this will increase your depth of field and further blur backgrounds! A wide angle lens will make for interesting dynamic portraits. A telephoto lens brings in the background offering another point of interest to a portrait.
A zoom lens 70-200 is a great choice, it will enable you to get really close to your subject making them the impact and complete focus of the portrait.
Be creative with your composition;
Think about how you position yourself when shooting a portrait, this will totally change the feel of your shot. It will totally transform and change the perspective of your subject - for instance shooting low will make your subject seem taller, tilting your camera slightly will make for more drama.
Add some light;
Using a reflector can really help to add some light. White gives a natural even light. Gold is good for outdoor shooting, giving a nice warm glow. Silver is more reflective, it bounces more light on to a subject and is cooler than white.
Focus your camera;
Setting your focus on your subjects eyes will help create intensity. For a less intense portrait a wider focus on the head is what you need.
With all this is mind you should be able to create some great portraits!