Lukaku is on-loan at West Bromwich Albion this season.
He said: "You have to be focused. I'm not wasting my time with my career right now.
"I'm 19 but I know what I want and I know what I want to realise in the future.
"I just want to be as complete as any player wants to be. I think Ronaldo never says something is perfect. He works on everything."