About 5-10 minutes before you want your grilled cheese, remove the cheeses and fillings from the fridge to allow the ingredients to warm up to room temperature which assists in the heating and melting of the cheese.
Butter the pan facing side of the bread with butter, just enough to cover the surface for an evenly browned crust without being overly greasy. Too much butter will make your bread soggy and overly greasy.
Applying butter to the pan is OK, but it is much easier to control how much fat you are using if you directly spread the butter on the bread.
Afterwards, proceed to build your sandwich with the ingredients you have taken out of the fridge previously.
Start by placing the sandwich in a cold pan, gas on low. Cover the top of the pan with a pot lid or something similar. The cold pan allows the heat to be gradually introduced into the bread and cheese without the pan facing side scorching and burning. The lid is to assist in the melting of the cheese.
Periodically check the underside of your sandwich once every 2-3 minutes until your desired brown-ness of the bread and your cheese has melted. Lifting the lid once in a while allows trapped steam to escape, allowing the crust to form and prevent your bread becoming soggy.If your cheese has melted but the bread has yet to become as golden brown as you wish, turn the gas up to medium to hasten the browning process.