Sterling arrived at City from Liverpool for £44million in the off-season but struggled somewhat in his first campaign at the Etihad Stadium.
The 21-year-old made just seven Premier League starts in 2016 but was still included as part of Roy Hodgson's provisional squad for the Euros in France.
Sterling was a star performer in England's 2-1 friendly win over Turkey on Sunday, and Hart believes the young winger will only continue to get better.
"He's got no point to prove, Raheem," Hart said. "I see Raheem work hard every day trying to improve.
"He's 21, he's fully aware of that and he's going to get better. And he's excited. He's an exciting footballer, someone I enjoy working with and I really want to do well.
"He was really good [on Sunday]. He got kicked to pieces because they couldn't deal with him, simple as that.
"I think maybe in a [European] Championship game a few of them would have been walking a lot tighter rope than they were.
"But it was good. I was excited to see it. It was tough for Raheem towards the end of the season - he wasn't starting games - that's gone and it's a fresh chapter.
"A fit and firing Raheem Sterling can change games."