When you first start off with portrait photography, it is all too easy to start believing that if you had a longer, faster lens your pictures would look better. Now, it is true that a shallow depth of field isolates the model from the background, but a seasoned photographed controls the bokeh area (the out of focus area) just to the desired degree.
Take for example this image of model Olha. While this image very much falls under the fashion portraiture category, to have isolated the model from the background totally would have made it a bit of an ordinary picture. Here, the background is very much a part of the composition and so it is retained in focus using subject-background distance and also aperture (it is photographed at f 10).
try shooting a few portraits keeping an interesting background within the depth of field area. Also, try using a middle ground by having an interesting background a little out of focus, but not totally. This works well for portraiture where you may want to retain the identity of the location, such as for travel related images.