According to BBC News, Hindi film music accounts for 72 percent of music sales in India. The Hindi film industry, also known as Bollywood, is huge and its songs, known as filmi, drive people to the theaters. As diverse as the Hindi film industry is, so is its music, which ranges from traditional Indian music to modern dance numbers. If you want to write songs for Hindi films, you have a wide variety of styles to choose from, but there are some conventions you should follow to be relevant to Hindi film audiences.
Familiarize yourself with the diversity of styles of Hindi film music. Study traditional Indian music as well as European classical and Broadway musicals. According to Gregory D. Booth in "Behind the Curtain: Making Music in Mumbai's Film Studios," the earliest Bollywood films focused mostly on traditional Indian music. In the 1930s, however, a new breed of directors, enamored with European classical music and Broadway musicals, came on the scene and merged traditional Indian music with these other styles.
Study the dramatic style of music that results from the merging of traditional Indian music with European classical and Broadway music, but stay current. Over time, Hindi film music has branched out into genres like dance-pop and continues to follow trends in popular music. Much Hindi film music today differs only slightly from straight pop music. It is upbeat and produced. Understand the conventions of pop music in your writing, but be aware of traditional Indian modes (raga) and rhythms, as they are still a presence in Hindi film music.
Write in several Indian languages, as well as English, interchangeably. The chief language used in Hindi films is Hindi, as it is the most universally understood, but many songs contain words from languages like Urdu, Punjabi, Braj, Rajasthani and Bhojpuri to reflect regional dialects as they relate to certain movies. Many modern Hindi films contain English words as well. Write the lyrics to reflect the part of the country in which the film takes place or to indicate a shift in mood or theme in the film.
Write lyrics that people can relate to. Many Bollywood films are melodramatic and revolve around love and estranged lovers. Other themes include family, God, religion and self-sacrifice. You don't need to have a professional or educational background to write Hindi film songs, as most are about love, but you should have an understanding of Indian culture so as to shape your lyrics for Indian audiences.
Familiarize yourself with Hindi and Urdu poetry, as many song lyrics contain references to Krishna and other religious elements. With the increasing presence of Western culture in Hindi films, it has become less common to include these themes, but they are still present. References to the flirtatious nature of exchanging glances are a common element of Hindi poetry and have made their way into Bollywood songs.