Fairy lights can be soft light or they can be a bunch of tiny hard lights, depending on how you use them.
A large soft light needs to be as homogeneous as possible. Meaning a large surface area that is evenly contributing to the output of light
This cheap softbox had bad diffusion and needed extra layers of inside to make it more homogenous.
See how the first one has a hot spot? But the one on the right is very even across the entire surface?
Your light source needs to feel like it is all one entity.
Dangling fairy lights are like a bunch of hot spots. If they are hung close enough, they can sort of team up as one light source, but you may not get a strong soft light effect.
However, if you attach your fairy lights close to a wall or a ceiling...
The light is going to bounce off the wall and create a larger light source. The wall itself turns into a secondary light source to help soften the light.
The big problem with string lights is they aren't terribly powerful. So your camera may struggle to get enough light and your photo may turn out noisy. You can help this by getting as close to the lights as possible so they are brighter relative to your camera.
But I actually think fairy lights are best suited for background lighting. When they go out of focus they look kinda magical.
And they can create a nice warm wrap of light around your head and shoulders.
So I would put the fairy lights in the background and then try to add an additional light on the front of you. You can bounce a lamp off a wall to get a larger light source. Or if you have one of those floor lamps, you can bounce it off the ceiling to fill your room with soft ambient light.
I've even bounced light off a $5 science fair board to get a large soft light.
The big problem with household lights vs pro lights is they aren't nearly as powerful. So it is more difficult to get the same results. But just remember, the closer you are to the light source, the brighter it will be. It may need to be *uncomfortably* close, but you can DIY good pictures with regular lights if you experiment.
