1. Everything must be done for Him only

    Do whatever you like or whatever may be easier for you to do, eat whatever you may eat, sacrifice whatever you can sacrifice, give whatever you may give in charity, and do whatever you may undertake in penance, but everything must be done for Him only. If you do business or if you accept some employment, do so on behalf of the Lord. Whatever you may eat, you may offer the same to the Lord and be assured that He will return the food after eating it Himself. He is the complete whole, and therefore whatever He may eat as offered by the devotee is accepted because of the devotee’s love, but again it is returned as prasada for the devotee so that he can be happy by eating. In other words, be a servant of God and live peacefully in that consciousness, ultimately returning home, back to Godhead.

    From Srila Prabhupada’s purport to SB 2.9.36