- The situation can be improved by removing the "casing" for the ceiling light to increase the light
- Use a white/bright background.
or place your subject near windows where the light will shine on their face etc.
Shooting with flash indoors. It will be best to look into bounce flash. It can be done even with on board flash. Just need to DIY a namecard bounce. Basically it's a white namecard infront of the flash that is 45 degree aiming the ceiling. But this namecard bounce will "eat" up abit of light as compared to using external flash where the head is tilted facing the ceiling. When shooting with flash bounced to the ceiling, need to take abit more care in PP where the shadows of the eyes, forehead etc gets too dark due to the light casting down from the top.
For post 18, shot #3, it's a common "problem" when using direct flash. (In my words) The background will be darken as your camera is "tricked" to shorten the shutter speed (lesser time for the background to be exposed properly) and the difference in the amount of light in fore and background due to the flash causes the background to be dark.
In cases like this, if you have the option to diffuse your flash abit. it may look better. Best is you can bounce your flash to the ceiling or "somewhere", where you can spread across the room/frame. When the flash is bounced to the ceiling, it will act like an additional lamp brightening up your frame, so you can use a lower ISO etc.