Cheese. Look at using a cheese like Harvarti, Gouda, Muenster or Fontina. These cheeses all have a softer texture which melts well.
Vegetables. Fresh fruits and vegetables can be a perfect addition by adding nutritional value and flavor. Examples include: avocado, apple slices, blueberries and cucumbers.
Bread. Select a whole grain or whole wheat bread for a tasty sandwich.
Spread. Traditionally, grilled cheese sandwiches are made with butter or margarine. If you choose to use butter or margarine, only use a small amount. Other options include coconut oil or olive oil. Add a small amount of oil directly to the skillet rather than spreading it on bread. Warm up the pan and oil, then place the sandwich in the hot oil.
Cook low and slow. You will get better results when using medium-low heat rather than rushing. If too high of temperature is used, the bread will brown quickly without thoroughly melting the cheese.