Having rarely shot in indoor studios besides at uni, I have spent my photographic career utilising natural light in my portraiture. However, during the winter months when the days are shorter and the weather is gloomier, indoor shooting often becomes your only option. It is still possible to use all natural light whilst shooting indoors if your location is particularly bright with lots of windows. Although, it is not always an option. When you're in this scenario you may find yourself struggling with your ISO or your shutter speed. When shooting portraiture you ideally want to stay hand held so that you can move around your subject with ease and you definitely want to keep your ISO as low as possible to avoid the inevitable grain.
Using flash is a completely different way of working. As soon as you bring in an artificial light source, your whole technique changes. You have to think about your shadows, where you want them to be and how harsh you want them. You suddenly have so much control over the situation it can be overwhelming.
I don't have much experience with using a flash gun in my work so I enjoyed pushing myself out of my comfort zone with some of my latest shoots.
I learnt that if your flashgun is facing directly towards your subject then your subject could become blown out and flat looking. It also makes the image look more unnatural and adds a dramatic shadow behind your subject.
The best way to position your flashgun is probably facing upwards towards the ceiling so that the light bounces off the ceiling and refracts back onto your subject. This way looks more natural and less harsh, however it could also create different shadows on the face of your subject. Make sure that all room lights and overhead lights are turned off, you don't want their glow to interfere with your colours or your highlights.
You have to balance out the settings on your camera and your external flash settings in order to get your image correctly exposed. Some rooms are much brighter than others so I can't tell you exactly what settings to use, but just keep playing around with changing different settings in your test shots until you find an exposure that you're happy with. Remember you can always keep tweaking you're settings throughout the shoot when you change poses and positions.
In the reel below you can see how when I photograph with the camera vertically to get a portrait image, I have my flash gun facing the wall so that the light bounces back onto my subject providing a soft and even light by lighting up the room.
You can see the results below.