I wrote this originally for the www.church-strategies.com newsletter, but since this is a question we get all the time, I thought I'd post the e-strategy that I wrote here. By the way, you can sign up to receive the www.church-strategies.com Newsletter here.
The #1 Factor to Creating a Culture of Evangelism in Your Church
I believe one of the most critical factors in creating a culture of evangelism is people seeing evangelism happening in the church. At Calvary Fellowship, we present the Gospel every week because we know there are people in the crowd who don't know Jesus. Thus, because we present the Gospel every week, people respond every week.
When your congregation knows that the Gospel is going to be presented, they will bring friends who need to hear it and respond. I talk about this idea further in our New Believer Follow System and How to Make Every Sunday Like Easter.
But take it from a guy who doesn't consider himself an evangelist but Pastors a church where over 800 people have come to Christ in the last 18 months: present the Gospel regularly and unchurched people will show up and respond.