Sacrifice is giving up something of value for a purpose beyond ourselves. We see it in a parent who gives up sleep, a person who donates time or money and a student who gives up entertainment to study. The Gita gives sacrifice a wide meaning and says that a life without any is hollow, while a life shaped by it is both harmonious and spiritually fruitful.
Gita 4.31 says a spirit of sacrifice is essential for both worldly harmony and spiritual advancement, so contribute something beyond personal gain through service, charity or spiritual practice. Gita 3.13 says that sharing what we have, beginning with our food, purifies a person, while living only for oneself is spiritually harmful. Gita 4.32 says that understanding the purpose and nature of sacrifice helps one become free from bondage, and that action done with awareness and dedication becomes an instrument of growth.
The Gita also recognizes many forms. Gita 4.25 says that different seekers approach spiritual growth through different kinds of sacrifice according to their understanding and practice, so respect diverse paths while staying sincere in your own. Gita 4.28 lists charity, austerity, yoga and dedicated study of wisdom, so develop a balanced spiritual life that includes service, self-discipline, learning and personal practice. Choose one form of giving you can keep up, and let it grow.