The ability to be keenly observant to the ordinary things in the world around you is a huge bonus as a lighting designer. After all, many times we're called upon to create artificial versions of ordinary things on stage using lights, such as sunsets, moonlight beaming through a window, the arc flash of a subway train moving along its rails, etc. Taking note of lighting in real-world scenarios and documenting interesting light you come across (camera phones are great for this) makes it easier to approach creating these looks from scratch when the time comes.
Good people skills off-stage, believe it or not, can also help your lighting skills on-stage. I'd say on a typical one-off, about 40% or less of my time is actually spent behind a lighting board. The rest of that time is often spent dealing with people, from confirmation phone calls with the guys at the shop who've packed my gear, to sweet-talking the maintenance staff at the venue to allow me to stay just a few more hours to program lights after everyone else has left. Having the maintenance staff on your side at a given venue is often paramount in having a smooth run. Tip: Pizza is cheap!
Holly Blomquist