For many, this seems to be something that is out of the question. However, it doesn't have to be. Some of the greatest preachers were street preachers. Jesus was a street preacher, the disciples, men like John Wesley, George Whitfield were all street preachers. Obviously you will want to go with some like minded brothers in the Lord who can assist, find an area where there are people gathered, and then lift up your voice like a trumpet.
You may start out saying that you are going to take advantage of your first admendment rights and that you would like to share a message of hope for those interested in hearing. Then a good way to start is to mention the things of the world and the horrific crimes that we here about, the wars and rumors of wars and all the seemingly helplessness. Then turn it to the things of the Lord preaching the full counsel of His word, such as; why is there evil, sin, then bring it home to them and their actions of breaking the law (God's law), that sin is personal to God, that all of us are accountable to a holy God and that He has declared we are separted, in need of spiritual life and without His grace we will perish. Then preach the cross and the need for man to repent and believe the Gospel.
May this help and encourage you in Jesus name.