Sometimes you have to be bold with your choice of lens. Choosing the wrong lens for an specific situation may bring added panache to your photograph. Lets say for example you choose a powerful telephoto lens or zoom, anything above 300mm for a portrait. This lenses, typically used for sports and nature photography, have the ability to compress distances between visual elements.
You would need to take into consideration the peculiarities of this lenses, for example since they are big and heavy, you would need a good support for your camera. My advice is to have a good sturdy tripod so the weight of the lens is not an issue. Another aspect to take into consideration is that most of them except for the very high end variety, the white lenses you see in sport events, are very slow in comparison to normal portrait lenses. What does this means, that the largest or fastest f:stop setting (@f5.6) is slower than the one you would normally have on a portrait lens(f2.8).
So you will need a good light source, either a nice sunny day or a good flash or strobe, in my opinion is better to have a good light source than to sacrifice image quality by using a high ISO setting.