The main thing you want to do is to make sure that you keep that tooth as clean as possible. After you have brushed your teeth, not hard on that tooth, and then rinsed with a mouthwash, mold a piece of dental wax, orthodontic wax, and or even candle wax over the tooth to close the area off where you lost your filling. Each time you eat and brush your teeth, you will need to replace the wax. The wax will fill the void, protect your tongue from any sharp edges, and will help to protect the remaining tooth structure.
You can eat on that tooth normally, just avoid eating anything hard like pretzels or chewing on ice and avoid sticky foods and snacks.