The Amish will not appear on your doorsteps to share the gospel or stand in street corners handing out tracts, neither will they go seeking converts to their faith.
They believe they will point more people to God simply by living a life different from the world, in nearly every way.
Their clothing, plain and what they think will not draw attention to ones self.
Living out the sermon on the mount. If Jesus taught it on the sermon on the mount you can count on them practicing it.
Marriage is a lifelong commitment, divorce is not an option. Matthew 5:32
They will not swear, as in giving an oath. Matthew 5: 34-37
They will not sue anyone. Matthew 5: 38-40
They go out of their way to return good for evil. Matthew 5:44
Giving alms after communion is not talked about, even husbands and wives don't know how much the other is giving. Matthew 6: 1-4
Prayers are either silent or from their little black prayer book. Matthew 6:6
They forgive those who wrong them. Matthew 6: 14-16
They don't spend a lot of money on things that aren't necessities. Matthew 6:19
They don't talk about their faith unless someone asks questions. Matthew 7:6
They obey the golden rule. Matthew 7:12
They believe that modeling their life according to these points will do way more for the kingdom of God than going out "witnessing" ever would. People will see their good works and glorify their Father in heaven. Matthew 5:16
We're no longer Amish, but we still apply these same principles to our life, in addition we are much more open about talking about Jesus and what He has done for us, and prayer has become much more than it used to be.