I know some people will scoff, but Lee Earle's
The Gentle Art of Cold Reading CD and booklet is not a bad introduction if you're not sure how far you want to go.
It deals mostly with the twelve classic Forer statements (general statements that people tend to believe apply to themselves). But there is also good advice on basic observation of things like clothing, jewellery, apparent educational level, etc. In this way you can begin to expand on the Forer statements and spin them into a more personalised reading. There's enough in
The Gentle Art to let you do relatively brief, shallow readings in situations like table-hopping or a fair booth.
If you want to get into meatier stuff,
Tradecraft is good. It's available from Trickshop as an instant download.
Actually, I see that Trickshop is selling both
Tradecraft and Robert Nelson's
Art of Cold Reading as a bundle for a very tempting price right now.
http://www.trickshop.com/cold_reading.html#both