i attempted to do this for my very first robot (which someday ill actually document).
the best way i know is to use the same method a bull uses to run down a matador . . . track the color red.
to be more specific, you wear a bright red shirt, and your robot has a camera running a very simple middle mass detection
on the color red. the centroid is fed to your robot motors, and it will follow you.
ive got this to work on two of my robots.
the harder part is to get the robot to go where a human can go, something i have yet to accomplish . . .