In your association with unbelievers do not allow yourselves to be swerved from right principles. If you sit at their table, eat temperately and only of food that will not confuse the mind. Keep clear of intemperance. You cannot afford to weaken your mental or physical powers, lest you become unable to discern spiritual things. Keep your mind in such a condition that God can impress it with the precious truths of His word. 2TT 551.4
Thus you will have an influence upon others. Many try to correct the lives of others by attacking what they regard as wrong habits. They go to those whom they think in error, and point out defects, but do not put forth earnest, tactful effort in directing the mind to true principles. Such a course often fails of securing the desired results. In trying to correct others we too often arouse their combativeness, and thus do more harm than good. Do not watch others in order to point out their faults or errors. Teach by example. Let your self-denial and your victory over appetite be an illustration of obedience to right principles. Let your life bear witness to the sanctifying, ennobling influence of truth. 2TT 552.1
Of all the gifts that God has bestowed upon men, none is more precious than the gift of speech. If sanctified by the Holy Spirit, it is a power for good. It is with the tongue that we convince and persuade; with it we offer prayer and praise to God; and with it we convey rich thoughts of the Redeemer's love. By a right use of the gift of speech the canvasser can sow the precious seeds of truth in many hearts. 2TT 552.2