The Correct Method in Calling to Allah

Question:
Sometimes I try to convince some relatives and friends to leave a bad job or to perform a duty, but I see that my approach achieves nothing despite my efforts in that regard. I ask for your advice on the correct method for calling to Allah?

Answer:
Guide them with verses and hadiths if you have them memorized, in a good manner, not with harshness or violence, no. With kind words and a good approach, "O Abdullah! O So-and-so! O Abu So-and-so! This is not permissible, it is obligatory for you to do such and such, Allah said such and such, the Messenger said such and such," according to the sin. If he is late for prayer, advise him to be consistent and remind him of the verses and hadiths. If he is undutiful to his parents, warn him about undutifulness to parents and that it is among the greatest of major sins.
Likewise, if he is dealing in riba (usury or interest) or drinking intoxicants, warn him. And if your words do not affect him, seek help from Allah, then from some of your good brothers. You and they go to him, you and your other brother, or your uncle, or your maternal uncle, or some of the good neighbors, so that you may advise him; perhaps he will respond to all of you, perhaps he will accept the truth, yes.