Chess can't be taught, it can only be learned 
Have them read, play, and review games. Both their own games, and master games. Usually you start with people like Morphy.
Reading would be like Dan Heisman and playing is preferably long OTB tournament games.
The teacher can provide useful materials (like books, and game lists) and occasionally some analysis. All the hard stuff though is done by the student, often alone, in quiet concentration.
How would you recommend teaching someone who used to be decent at chess how to play if they have not played in years?