Is simple: welcoming the stranger by attending to their needs first.
I have been visiting churches during this sabbatical. (This is always the most fruitful activity of sabbatical).
And not been too impressed with the welcome, frankly. Tools seem to be in place, but the spirit is all wrong.
For instance, a friend and I showed up in a UU church where one came out of the cold into a foyer. Ushers stood in a line perpendicular to the doors, and handed us programs with a perfunctory smile....but didn't catch on to our "what now?" looks. It wasn't at all clear from them, from architecture or signage where the sanctuary actually was. We looked around, bewildered, and nobody rescued us. Finally I turned back to the usher and asked him which way to the sanctuary. "Oh, are you visiting?" he asked. "Here, here's the welcome table". He handed us over to a woman standing behind the table. Nothing was clearer than that her only sense of what she was supposed to do was get our information....and entire page of information. She handed us a notebook and a pen and then remembered to say good morning. She pointed out name tags.
I'm from out of town. I didn't need to be followed up on or to get a newsletter. I came to worship that day. That's all I did, and that's all I wanted to do. It happens that I'm a UU...I knew I'd be in tune with the message at this church. . If I'd been a seeker, I'd have been even less interested in giving my information to these people...until I was sure I'd want to come again. But short of being rude, it was impossible.
The moral of the story: Smile and guide visitors on their way in. Give them whatever information they ask for. Get contact information on their way out....when and if they want to give it to you. Better Yet, put a "Thanks for Visiting Us" link to your website in the order of service explaining that at this site, visitors can give feedback, leave contact information, and ask questions. (if you have lots of elderly visitors, you can also invite them to do this after the service at the visitor's table.)
For a humorous look at things from the visitor's perspective, check out this little video which comes to us from the Evangelical world...but parts of it are oh, so, pointedly true of us, too!
What if Starbucks Marketed Like a Church?
P.S. Architecture and signs are really important in giving newcomers a clue as to what they are supposed to do. If you are not blessed in this way, your greeters and ushers can be on the look out for the bewildered or even standing in such a way that they make clear where a person is supposed to go. For most people, nothing gets them started off quite so badly as feeling like an idion...