Thats a hard question, with no true answer, alot just comes from doing alot of paintings, so the simple things get easier so you can focus on the harder parts.
But a good way to think about light is the same way they think when they do movies like Toy Story with a 3d programs, you have Ambient occlusion, its creating soft shadows everywere were light has hard time to reach, so you can for example use that in the corners of a room.
There is ofcourse more too, and I dont know if it would be the best way to start, but thats kinda how I see things now, it really helps breaking down things from photos so you can remember and understand it.
But also I use alot of reference if there is something I dont know, or simply want to make the painting more intressting.
Hm, looking at alot of good paintings and photos and try to figure out and understand them is important.
I guess when it comes to color/light, I'm having trouble coming up with ref that fit my initial intentions in terms of mood/setting. And thus I'm a bit puzzled as to how use the casual ref I stumble upon. But I must not be putting enough thought into this.
Good show! I like the 'vintage' looking texture on the wood; worn and old! Also the house 'scene' in the background is spot on; you just used the right amount of DOF to keep it in focus with the foreground - well done!