Your domain, page content, and website code will only take you so far. External factors can determine the majority your rank in search engine results pages. By default, the search engines don't trust your website. To build that trust, you need inbound links from reputable websites. These are in essence, referrals from trustworthy websites.
The easiest way to get some inbound links is to add a link to your website from your existing business pages on Yelp, Citysearch, UrbanSpoon, and local newspaper listings. You will need to contact these websites directly for information on how to add your link. This shouldn't cost you any money, although they may try to get you to advertise.
Another great source for inbound links is daily deals sites like Groupon and Living Social. When you have a daily deal on one of these websites, you will get an inbound link from the deal--a permanent page with lots of great keywords about your restaurant and food. However, you should proceed with caution, as daily deals can be very expensive to pay for, and may actually harm your business if not utilized correctly.
Does your restaurant have a public Facebook or Twitter page? If so, be sure to add a link to your website on the profile. One thing to remember with Facebook pages is that they need to be publicly viewable for the link to be visible. To check if your Facebook page is publicly viewable, just log out of Facebook, then go to your Facebook page. If you can't, you will want to change your business's settings.
One last way to get inbound links to your website is through local (and national) food and restaurant review blogs. If your restaurant is new, or if you have a great new plate on your menu, you may want to email or tweet to the blogger directly, politely asking for a review or mention. Don't forget to give them your web address!
You may be tempted to link to your website in the comments of a blog, but please keep in mind that a) people don't appreciate spam on their blogs, and b) the comments sections of blogs usually enforce a special kind of link that doesn't count towards your search engine placement. The links that count have to come from the blogger in their article content, not in the comments area. This doesn't mean you shouldn't comment on their blog; it just means that any links you put there will not necessarily help your rankings. Links can get you some traffic though, so if your comment is relevant, it can still help business.