According to the official Catholic handbook (enchiridion) for indulgences, "an Act of Spiritual Communion, according to any pious formula, is enriched with a partial indulgence." Non-Catholics are also welcome to say this prayer assuming they agree with the statements.
You can recite it as often as you want. Similar to eating the Holy Eucharist, this spiritual communion prayer strengthens us, but obviously eating the Eucharist strengthens us far more.
SPIRITUAL COMMUNION PRAYER
My Jesus, I believe that You are present in the Most Holy Sacrament. I love You above all things, and I desire to receive You into my soul. Since I cannot at this moment receive You sacramentally, come at least spiritually into my heart. I embrace You as if You were already there and unite myself wholly to You. Never permit me to be separated from You. Amen.