My dad taught me how to make a proper sammich. I couldn't have been older than six years old. To make a proper sammich (to his liking) you need to have a toaster oven.
Step one lightly toast both slices of bread
Put the meat on one slice and the cheese on the other
Return the two sammich halves to the toaster until the cheese is melted
Remove and add your cold ingredients (lettuce tomato mayo mustard)
FTR there are a few ways to get on my sammich list. I eat and make other types of sammiches but to me this will always be the "proper" way to make a sammich.