I probably spend 40% of my time in TS3 actually playing with my sims. The rest of the time, I create things. I'm not at all good with houses, so if I'm playing the sims, you can typically find me in CAS. When I first started playing around with CAS, I got quickly frustrated, I wanted to make a vampire character, but none of the default faces were threatening. As soon as I took a look at the advanced face tools, I was extremely intimidated; not because of the sheer amount of tools, but because I had no idea which tool did what. I had no idea what raising the nose of my sim would do for his overall appearance.
Psychology has always interested me, and I like to apply it to my everyday life. I did some research on the internet and found some very helpful links on facial body language and color psychology.
If you like to make a wide variety of sims, I think these links will be quite helpful, especially if you want to make evil or threatening sims. The default faces are cheery and kid friendly, not at all befitting a serial killer.
Enough talk, here are the links.
http://changingminds.org/techniques/body/parts_body_language/face_body_language.htmhttp://www.infoplease.com/spot/colors1.html