1 flash photography is all about balancing your ambient light and your flash. learn how to balance, use your flash as a fill, subject placing using the sun and the available light and you are in for a good trip.
In studio, 1 flash is always a pain in the ass and you are limited. large white board or a cheap
ebay reflector is a good options if you are financial tight.
here is used the sun as a back and rim light then i used a small 24X24 softbox with a speedlight to fill.
here, same softbox for fill and a small beam of light coming from a higher windows as a hair light.
I was able to get a bit a ambient light by shooting a large aperture, slower shutter speed and pumping the iso a little bit. adding a bit of fill using flash with these settings was quite easy as it doesn't take much power to light a scene like this at F3.2 1/200 and iso320.
In this shot, i could have measured 3 different light output on my model but only using 1 flash. i used the ambient light, got the flash in at maybe 1.5-2 stop more than the ambient and was lucky that the beam of sun coming from the windows was about another stop higher.