As soon as you know your audience, you should have a good idea of which deals will be attractive to them. Wellness and restaurant deals are a good start (as proven by Groupon). If you would like to follow this route you may also add various cool activities like yoga/dance/cooking classes.
Entertainment deals like cinema or theater shows and sports/musical events may be a good fit. Sure, top star performers or world cup championship competitions get a lot of press coverage, but if there is a local competition or some obscure garage band, or classic opera performance, or perhaps local artist exhibition — they will be happy to get more people to visit them. Make it clear in the deal terms that the coupon is only valid for certain date of the event and give it a shot.
Getting deals from local vendors should be straightforward: as soon as they understand the idea and realize they do not have to pay anything and will get guaranteed visitors. Open your city's "yellow pages" website and start calling. Focus on recently opened places, as they will be naturally interested in expanding their user database.
You may also check vendors recently featured on other daily-deal sites (especially Groupon). If they liked it, they will be looking for any opportunity to get featured once again.
Make it clear for merchants that because of the huge discount they will not make much money from the deal. They should think of it as an investment into getting new customers, an advertising expense with guaranteed result.
Make coupons only valid for off-peak hours, and you can get decent discounts, as the place will be underfilled anyway, so vendors have nothing to loose.
Try to structure deals to make the coupon price as low as possible. First few deals should not exceed $20 per coupon, and even better if they are under $10. Remember, the lower the price the more purchases you will get and making your subscribers base growing is the primary goal in the early days of a daily-deal website. If it's a gym deal make it one-day access rather than one-month access. It goes without saying that the discount should be at least 50%.
And, finally, make sure that the discount is real, that is there is no way to get the same service at the same or better price. Because your visitors will find it out and it will harm your reputation.