A classic portrait is generally a head and shoulders composition, but can refer to a number of different situations, from professional head-shots to capturing your subject's personality. However, classical portraits are usually taken at a distance from the subject to ensure that they do not feel uncomfortable. An ideal lens for this type of photography would have a focal length in the region of 85mm with a wide aperture (f/l.2 to f/2.8). A lens of this focal length lets you work at a comfortable distance and provides a flattering perspective for your subject. A wide aperture also allows you to work in low light conditions, whilst separating your subject from the background by providing a shallow depth of field. Standard zoom lenses with a wide aperture can also achieve this.
When you want to capture people naturally in the moment, you need a lens that will allow you to shoot close-ups from a distance. The ideal lens would be a zoom lens in the 70-200mm range (shooting at telephoto), as this will get you closer while giving you the ability to capture your subject unaware in their natural environment.
Group shots can feature anything from three to three hundred people in a variety of settings. The amount of people you are trying to fit into the frame, will determine the lens you Il need. The larger the group of people, the wider the lens you will need. A wide-angle lens in the 16-35mm (full frame) range will help to fit everyone in the frame with ease. For smaller groups a standard fixed focal length portrait lens in the focal range of 30mm-85mrn, will be enough to fit everyone into frame.
When you want to capture more of your subject's story by photographing them in their environment, you can use a wide-angle lens to increase the field of view and fit more of your subject's surroundings in frame. However, wide-angle lenses can distort the physical relationships between objects, but as long as you're aware of this and how it affects your shot, you can use it to stylistically create images that you simply couldn't capture any other way.
Whether you are in a studio or on location, you can use different lighting styles to complement your model. This can span from shooting at different times of day, to using a reflector to highlight the features of your subject.
You need to plan how you want your subject to fill the frame. This doesn't limit you to only using one third of the frame, especially when capturing close ups. You should experiment to see how you could fill the frame in interesting ways.
When planning a portrait shoot its important to consider the background of each set up. You want to use backgrounds with structures and colourings that will compliment your subject, but not draw the eye away.