Arun's article on CLO:
http://main.uschess.org/content/view/10298/585
He's too modest to point out that he ripped it up after a 15-year hiatus!
I agree tactics are important, also adult students seem to pick up rather quickly on positional concepts, which just makes tactics more important. But besides tactics, calculating itself is key (identifying candidate moves, trying to identify critical moments when you must calculate longer and harder than usual, looking for loose pieces, etc, Forcing Moves is a good book that addresses this, Think Like A GM too, though both books are somewhat advanced.)
Also it's important to make sure chess study does not make you play worse. Like in poker, a little knowledge can be a dangerous thing and I think adults are especially prone to this.
I like to think of chess skill as combining your instincts with active thinking when your instincts are insufficient. Instincts alone make up the majority of skill- that's why a 2400 player can beat 20 1800s in a simultaneous exhibition, without thinking at all.
Best, Jennifer