Before you can unlock this achievement you will need to have unlocked all the story characters, the vast majority are unlocked via the story itself but there are a few from random encounters. There is a list here of the characters and it shows which mission unlocks them (and of course details that mission) http://gta.wikia.com/wiki/Director_Mode
I only did the story and Kifflom and I was only missing 2, Beverley and Mrs. Thornhill.Dylan XBA also notes that Dr Friedlander is also missable but https://www.trueachievements.com/chasingghossts.htm confirms you can visit at any time to unlock him
Once you have them all unlocked, whilst story mode is loaded up press
and scroll right using
to the 'Rockstar Editor' menu and press
to enter. Choose 'Director Mode' from here and accept the launch.
Click actors and pick any of the actors in the Story characters menu.
Once the mode loads the achievement will pop, BLAZE VII
notes that this one might have a little delay before it pops.