First thing you will want to do is to plan a meal. Try to plan it early enough in the week so that if it is something that you have never prepared before you can do a trial run before the actual dinner. Follow the K.I.S.S. method. This means Keep It Simple Stupid. By this I mean if you have never made Beef Wellingtons, this might not be the best time to experiment with it. Find a recipe with cooking techniques that you are comfortable with and go with that.
Next, you are going to want to set the mood. Candlelight, dim lights, sitting across from each other or to the left or right of your dinner mate, that is all up to you. If this is a person that you are familiar with the closeness may be welcome, however if this is someone that you have recently met then give them a little space. Definite dos are setting the table, with a table cloth. Flowers are ok, but if you are sitting across from each other don't place them in the middle of the table.
Let the guess pick the music, you can have something playing when they arrive but invite them to check out your CD collection and pick something they like. At this point it is a good idea to offer something to drink.
Always serve the meal in courses, such as salad, soup, entrée and dessert. This gives you time to get the next course ready without leaving your date alone in the room. For example while you are eating the salad have the soup heating, and while you are eating soup heat the entrée, and so forth.
Finally the most important thing to do is to relax. The night will go much smoother if you are relaxed, the conversation will be better, the food will taste better and not to mention the confidence it will give you to tackle even bigger dinner parties. Have fun and be creative this will make the evening more exciting and memorable.