Dr. Martin Luther taught extensively about the best prepartion for those coming to Holy Communion. Early in the Reformation (1518) he wrote a concise account of his views to Cardinal Cajetan.
Not by any preparation or work of your own do you become worthy and fit to partake of the Sacrament. This takes place through faith alone. For only faith in the Word of Christ justifies, quickens, makes a man worthy and well prepared. Without this faith all other efforts beget either presumption or despair. For the just shall not live by his preparation but by faith. Therfore you must not hesitate at all because of your unworthiness; for you, an unworthy person, come to be made worthy and righteous by Him who seeks to save sinners and not the just. (What Luther Says, para 2526, page 814)
In a Maunday Thursday Communion sermon (1523) Dr. Luther anchors the reason for his teaching as above in the truth that in the Sacrament it is God who works, not us.
No greater shame and disgrace can be heaped on the most venerable Sacrament than merely to consider it a good work; for a good work is something I can do to another, and it must be an act I perform. But the Sacrament is not my work but God's work, with which I merely let myself be served and from which I receive a blessing. (What Luther Says para 2506, pages 808, 809)