There are so many elements that would impact my answer, I hardly know where to start. It all depends on your location, the type of food you serve, the price category, local competition, the reputation of your kitchen, past PR coverage, name recognition and more.

Most of all, I'd like to know what brings diners in for dinner, who they are (demographically), and if you have an entirely different crowd at lunchtime.

For now, I'd say build on your strengths by figuring out who frequents your restaurant for lunch now and why. Then pick tactics--which may be anything from direct mail to radio--that reach more people like them.