Flash photography consists of elements like shitter speed, aperture, flash output and ISO. Here’s what each element does.
Shutter speed takes the control of the ambient lighting
ISO defines the overall sensitivity of the rest of the parameters
Aperture takes control of the depth of field. In addition to that, it defines the amount of light that affects the scene
Flash output is the specific amount of power generated as light
Bu changing the parameters mentioned above, you can expect to create a more natural, realistic light. However, if you can use a large light modifier, you can expect much better results with a softer flash.
The most important thing you should consider to create a more natural flash is proper positioning. You should place the flash above the portrait’s subject (not directly above though). In other words, place the flash at an elevated position and direct it towards the portrait at an angle.