With mesh-lighting, you mean some specific assets?
I think I might also have a problem with the "where" to place a light to get better results. What I did in this room was to place some lights on the ceeling to get a well lighted room as I don't want it too dark and then I added a HDRI as a source of light from outside the windows.
For this render I added lights from behind the character, but not sure if that was a good idea xD
Not any "specific" asset. Mesh light can come from anything, including default primitives, like a plane, or a sphere, or a cube, or, basically anything you want it to act as a light source.
Basically, let's say you want to use a default primitive cube as a mesh light... select the said cube, go to the surfaces tab, and, using the default daz uber iray palette, load "emissive" onto it. And, now it's a light source, it emmits luminosity to the area. If you want to be more advanced with it, you can load an image to the emission color value, and use that as an emission base. Any image, but, as you'd guess, the brighter, the better, and, if your hardware (mostly your VRAM) allows it, google for free HDRI maps, to use as emission images.
That above applies to all types of mesh lights, like a lamp, or a neon tube, or a neon sign, or, basically anything you want to glow and emit light. Even portions of a character's skin, with the right use of masks to block/allow emission per surface pixels
