Though Holy Communion is not absolutely necessary for salvation, yet without the reception of its graces it would be difficult to resist grave temptations and avoid mortal sin for any length of time.
From the Gospel of Saint John, 6, there is the Divine command to receive Holy Communion worthily, which binds in any danger of death and some time during one's life.
The Church, confirming this Divine command, adds besides her precept of Paschal Communion under pain of mortal sin.
She further exhorts all the faithful, who are properly disposed, to receive frequently, and even daily, but not more than once a day.
The proper disposition as indicated by Pope Pius X requires nothing beyond the state of grace (freedom from mortal sin) and a right and pious intention in communicating, e.g., of honoring God, increasing in charity, overcoming faults, etc., and not merely from routine or vanity.
It is recommended, however, to keep oneself free from venial sin, at least from those fully deliberate, and from the affection thereto, and to seek the advice of one's confessor on the frequency of Communion.
New Catholic Dictionary