Strangers are a slightly more difficult proposition, because although a bare minimum of courtesy and politeness can be managed by most people, we are generally less tolerant with, and certainly less trusting of people we do not know. Our own insecurities cause us to be wary of strangers and disinclined to get too involved with them.
Some people will help strangers; others will not, as we see in the story Jesus told about the Good Samaritan. The Bible says in Galatians that we should "not grow weary while doing good for in due season we will reap a reward if we do not lose heart. Therefore as we have opportunity, let us do good to all, especially those who are of the household of faith." This is what I believe God expects of us and although it won't make us good, it will make us better.
The 12th chapter of Romans is arguably the best snapshot of Godly
behaviour in the Bible. It should be mandatory reading for everyone. Paul writes, "Do not be overcome by evil but overcome evil with good." (v. 21) "If your enemy is hungry, feed him. If he is thirsty, give him drink." (v.18) "If it is possible, as much as depends on you, live peaceably with all men." (v.18) Measure yourself against this criteria and you will quickly be forced to agree that you, and everyone else, falls short of the glory of God. There are no "good" men. Even Jesus, when addressed as Good Teacher, rejected this appellation by saying that only God is good.
If this sounds too hard, that's because it is. It's too hard for you, for me, for anyone. It's really not possible for men to live this way except they be filled with the Holy Spirit. Finally, remember this, even if you pass this test and can be good to not only your friends, but also to strangers and enemies, you still won't be anywhere near as good as God.