During the second visit of Sri. M, the author of the Gospel of Sri Ramakrishna (Sri Ramakrishna Kathamrita), in reply to M’s question, Sri Ramakrishna gave five instructions to be followed by spiritual aspirants.
M. (humbly): “How, sir, may we fix our minds on God?”
(1) “Repeat God’s name and sing His glories, and
(2) keep holy company; and now and then visit God’s devotees and holy men. The mind cannot dwell on God if it is immersed day and night in worldliness, in worldly duties and responsibilities;
(3) it is most necessary to go into solitude now and then and think of God. To fix the mind on God is very difficult, in the beginning, unless one practises meditation in solitude. When a tree is young it should be fenced all around; otherwise it may be destroyed by cattle. “To meditate, you should withdraw within yourself or retire to a secluded corner or to the forest.
(4) And you should always discriminate between the Real and the unreal. God alone is real, the Eternal Substance; all else is unreal, that is, impermanent. By discriminating thus, one should shake off impermanent objects from the mind.”
M. (humbly): “How ought we to live in the world?”
Sri Ramakrishna: (5) “Do all your duties, but keep your mind on God. Live with all with wife and children, father and mother and serve them. Treat them as if they were very dear to you, but know in your heart of hearts that they do not belong to you.”
Swami Dayatmanandaji of Ramakrishna Math gave a talk explaining these five points in detail, which was published in Vedanta Kesari. You can find the transcript here: http://www.estudantedavedanta.net/The-Five-Commandments-of-Sri-Ramakrishna.pdf