**SPOILERS**
Alright, this is a pretty straight forward achievement. After you get Johnny from his simulation, meet him on the ship, talk to him, and do the romance to get it out of the way. After that, go into the simulation and just keep doing his missions (which are found under Side Quests in the Quest menu). Achievement will pop after all of his missions are done, and he will also be a "Super Homie" after the first quest.