How can we perform an act of charity that truly has value and is not considered nonexistent?

Answer from the V.M. Samael Aun Weor and the magazine.

Any act or “Pardat,” whether it be Jñana or Ritual, Charity or Austerity, if done without Faith, is considered “ASAT” (nonexistent). It has not been properly done and bears no fruit here or in the Hereafter…

Samael Aun Weor.

Answer from the magazine "The The wisdom of the Being.".

According to the Bhagavad Gita, charity is itself a spiritual practice (Sadhana), since when we give, we experience a small liberation, a small death of attachment. The hand that is freed from material bonds is also freed from spiritual bonds, helping us to grow inwardly. To learn to give to the person in need, at the right time and place, we need to learn to listen to the Voice of Silence, to our Father who is in secret, who manifests through the tranquil heart. The inner work of purification is the path; meanwhile, let us seek to practice charity with sincerity, wisdom, and discretion. This implies not neglecting our obligations as good fathers, good sons, good brothers, etc., because then what we assume to be charity would become a crime against our family.

The Magazine "The Wisdom of the Being" 108: "The Three Charities."