Johnston shaped as Taylor Walker's likely replacement early this year after dominating in the SANFL, only for a fractured leg to sideline him for two months.
The 22-year-old told afl.com.au the time off allowed him to reflect, and he said he returned from the injury with a greater drive.
"It was during that time that it clicked if I didn't pull my finger out and play good footy towards the end of the year, next year I'd probably be flipping patties at the local service station in Port Pirie," Johnston said.
"I had a couple of quiet games, but I was pretty happy with my good performances."
The big-kicking forward played the last five games of the year for the Crows, booting 11 goals and showing huge improvement in the defensive side to his game.
His six-goal haul against Melbourne in round 22 saw coach Brenton Sanderson insist he'd be offered a new contract at West Lakes.
Crows list manager David Noble said with further development Johnston could become a cornerstone of the club's attack.
“Lewis showed some very promising signs when he got his opportunity late in the season," Noble said.
"He’s a dangerous forward who capitalises in front of goal, and we think has the potential to become a key component of our developing forward line.”