ah, no rules for this. I don't mind what you put in there.
The key to an old TG0.9x look is just in the atmospherics. People usually made high contrast skies, light beams, and there was no GI. There was either an equivalent of fill light, and/ or something close to ambient occlusion.
Just look at the planetside TG0.9 gallery, there should be some of these in there.
cheers,
Frank