Marketing ideas to promote a business?

[Slice]

Hello!

I work at a dental office and we're trying to come up with ways to promote our practice. It's a small office with one dentist and one hygienist (that comes in only 2 times a week). We open on Saturdays (which is our most liked day).
We're trying to attract new long-term patients.
How can we do that? What can we do?

It's illegal to provide free stuff (example, free gas card) for new patients here. So we have to be very creative.

Thanks for you help!