James 4:6 "God opposes the proud but gives grace to the humble."This is the foundation to being able to receive grace.
As far as treating people, are they simple, foolish or evil? Applying wisdom i.e the book of proverbs to figure out what you are dealing with is a good start. If people meet the conditions of being able to receive grace, i.e humility then we have a conversation and we can "faithfully administer God's grace in its various forms." I peter 4:10. Then God's wisdom through prayer and hard work follows.
Here is a brief overview of how I see God implementing his grace.
When we think of Law and Grace we can easily drop into just the Pauline views on the subject rather than take a whole bible view. If we take a broader approach, we can learn more about how God applied law and grace to the whole human race.
God's process was to begin with a relationship in the Garden. God was with them, God was near. That got disrupted to say the least, now we were on the trail of choices and consequences, then structure with ten commandments and Levitical laws. All of these ordinances were to visibly show that God wanted to live among them. We still didn't get the meaning of God's grace and we see that "Those who cling to worthless idols forfeit the grace that could be theirs. (Jonah 2:8) This sums up the experience of the Israelite/Struggle and walk with God.
Now, we move to a situation that God has to send Jesus in person to walk and dwell among us. That still wasn't enough - we crucified him! Thankfully, God raised him from the dead so that Jesus continues to live, and that favor of God gets extended to us through his mercy and compassion. God sealed us with His Holy Spirit and now we can administer the grace we have received.
I think that we do people an injustice when we require them to act differently than what they show themselves to understand. Rules and laws are there for our/their protection when we don't have that knowledge or forethought within ourselves. When we learn the basic rules, its only then we progress to applying the principles those rules were based on.
Isaiah 28:9-11 "Who is it he is trying to teach? To whom is he explaining his message? To children weaned from their milk,to those just taken from the breast? For it is: Do and do, do and do, rule on rule, rule on rule;a little here, a little there." Very well then, with foreign lips and strange tongues God will speak to this people"
"Those who cling to worthless idols forfeit the grace that could be theirs. Jonah 2:8
God will teach us, the question is will we learn?