One of my favourite lighting setups to use is a single octagonal soft box placed almost directly above the model pointing down on them as a 'key light'. Keeping the model a good meter or so away from the back wall will prevent a lot of light from spilling on to it even without an egg shell grid on it. I use the set up a lot (probably too much) but I think it has such an atmospheric look and feel to it. The lighting diagram below shows the setup.
We can see that is does place quite a lot of shadows under the models chin as we might expect but keeping the soft box as close to the model as possible not only keeps the light spill onto the background at a minimum it also softens the shadow still giving a pleasing effect.
I usually use this setup as a starting point and then look to build on it. One of the first things we can do is to try and get a bit more light on the model's face and possibly get a bit of a catch light in the eye. We can add a second light with a small reflector and grid to focus it on the model's face as a 'fill light'.
As we might expect, even with the flash power of the new light at its lowest, the face is now a little over-exposed so to compensate for this we can reduce the power of the key light. In the setup below I have reduced the key light power by a stop.
The exposure on the face is now much better. Just to show how we can add a third light into the mix though we could add a second fill light to the right of the camera to lift the shadow on the back of the dress and hair just to add a little separation. We will use a relatively large rectangular soft box to illuminate the length of the model. This could cause a lot of spill onto the background, depending upon its angle, so we will add an egg shell grid to it to keep the light in the direction of the model.
This has lifted the shadow on the back of the dress and given it separation from the background. It is not always easy to see what effect a light is having and one thing I would recommend is always seeing what each light is doing individually. In the diagram below I have turned off the key light and the first fill light just so we can see the effect of the second fill light on the back of the dress.
Of course what lights you use is purely down to the look you want to convey and, like I said at the start, sometimes I just prefer the single light but it is always worth having a play - you never know what you might discover!
Finally, just for fun, got an extra light? Well, we could do something with our dark background couldn't we? Let's just put a light with a red gel up against it to add a little atmosphere.