Reach Australia have a helpful article on “How to run an effective Evangelistic course“.
Here is an extract from the section “Advertise”:
Advertise
How will you advertise your event? Considering most guests will attend through either personal invitation from a Christian, or through hearing it advertised on a Sunday they happen to be at church, most thought should be given to galvanising your congregation, and equipping them to invite people they know. You will need to start advertising up the front during Sunday services from approximately no later than 5 weeks out of the event. Provide post-cards with the date and times of the event and place them on seats for 2 consecutive weeks. The announcement doesn’t need to be long or emotional, perhaps something like;
If you’re a visitor or a guest here today or perhaps you’ve been coming here for a while but you’re still unsure where you stand with God or perhaps you’re really not sure about the truth about Jesus we’d love to invite you to our upcoming Explaining Christianity course. It starts on Tuesday, 19th October, and runs for 4 Tuesdays. Come along, have some coffee and dessert and ask any questions you want or maybe, if you want, just come and listen. If you’d like to find out more, ask me after the service, or go to the info desk.
(tip don’t tell people to ‘speak to pastor X’ or ‘chat to Rev w’ because if they’re guests: they don’t know who that is!)
Your preacher should also look for opportunities to encourage people to attend in his sermons, perhaps after an explanation of the gospel.
Of course, there are other means of advertising that can and should be employed: your website should have updated and clear information, your social media presence should also promulgate the course.
However, make no mistake it’ the people sitting in front of you every Sunday who will bring the most guests along: and so every opportunity to actively individually or corporately encourage them to bring people should be taken.