The 52-year-old star made his Bollywood debut in 2001's Everybody Says I'm Fine!.
He told The Times of India: "Once, Naseeruddin Shah told me that the wafer shop was the best acting school that I could have attended. And I completely agree. I observed every customer very minutely and picked up some quirk or the other.
"Later, I used those experiences while playing different characters. Then there are characters for which you need to do some research. For instance, during Khosla Ka Ghosla, one of my most popular films till date with audiences, I studied quite a few land property dealers.
"Our film industry as well as the audiences are now open to unconventional pairings and subjects, which has aided my journey greatly. Even five years back, there wouldn't have been many takers for a film like Shirin Farhad Ki Toh Nikal Padi."
Irani recently admitted that he finds it confusing when actors avoid the paparazzi.
He will next be seen in the romance Shirin Farhad Ki Toh Nikal Padi, which also stars Farah Khan.
The actor plans to direct his first feature-length film later this year.
Watch the video for the title track of Shirin Farhad Ki Toh Nikal Padi below: