Just read another thread about someone didn't know how to follow and seemed a lot of people didn't know how to. Not as easy as FFXI but this also worked in FFXI as well as FFXIV.
1. Lock onto the person.
2. As they are moving you follow them.
3. While locked on and following them hit the run key. (I don't know which one is the run key. I configured a controller so you're on your own there)
Maybe they will implement a simple /follow later, but this works.