Want to get long-lost customers back into the fold? Why not send a card to customers you haven't seen in a year telling them they've been missed and that you'd love to see them again? Offer a "welcome back" discount as an incentive. You can give returning customers a dollars-off incentive, a percentage-off offer or any other deal you can think of.
You might even want to take it a step further by trying to determine why those customers stopped doing business with you in the first place. If you know they were unhappy about a particular transaction, felt they didn't get proper service or were disappointed with any other aspect of your business, acknowledge that fact and assure them that the matter has been addressed and corrected. Be sure to offer your incentive along with your apology.