Make yourself glamorous, and then go out of the house for the dinner date. If you are female, then also you wear a nice dress and use tantalizing perfume that can impress the partner.
When you are planning a proposal, you have to take a look at the place where you will have dinner. You can choose a rooftop restaurant, a poolside restaurant.
You have to tell something about yourself and also have to learn about your partner. What she wants, what she loves to eat, something intensive.