Find out if your church has some materials to letterbox in your area that can invite people to something running at your church, like an evangelistic series, Bible study or church social. Otherwise, make some invites up yourself. Then obtain a bundle of them and go forth and letterbox! Invite a family member or friend to come with you for an added social element. Pray for occupants of the houses as you go and make sure you respect the "no advertising material" requests on letterboxes.