When I got my first job at a bike shop, it was because the shop owner had put a coupon in the Val-Pak mailer, and gotten lots of tune-ups as a result. The Val-Pak is one of those envelopes full of coupons from local merchants, maybe your region has something like it.

In his case, he had a coupon for a free pack of four or five assorted stickers for kids, a coupon for a free saftey inspection (somewhat of a gimmick, since we'd do this anyway), and a coupon for $5 off a tune-up.

The other notion I just had: get peoples' email addresses when they bring bikes in for repair. Have a legal pad under the counter and ask a few customers if they'd be interested in getting an occasional email announcing sales or specials. If the response seems encouraging, you can start an email list and perhaps they'll forward them to other enthusiasts once in a while. Golden rule for email: be extremely brief and to-the-point