April is grilled cheese sandwich month.

Here are great articles on the perfect grilled cheese:
www.closetcooking.com/2011/10/perfect-grilled-cheese-sandwich.html
www.huffingtonpost.com/2013/08/27/perfect-grilled-cheese-formula_n_3824935.html

Now, the basics:

2 ounces of cheese per sandwich and 2 pieces of bread- allow 1 per kid and 1 1/2 for adults.

Use a warm, not hot, griddle. Use a 200 degree oven to keep warm or to soften cheese. Cooking time depends on the cheese. American cheese slices will take less time to melt than harder cheese like cheddar, figure a minute or two on each side.
Cover, not tightly, to generate more heat to melt cheese, if you like it a bit soft.

The cheese
The kids will like a thick slice of American cheese
Dry, crumbly, fresh cheeses like goat cheese won't melt properly. Ditto for overly aged cheeses like a parmesan or hard Pecorino, or aged cheddar. For the true classic American style, nothing works better than ultra-gooey, not-too-sharp American cheese.
For grown ups, though, or serious eaters, a young cheddar, jack, gouda, Swiss-style cheeses like Gruyère (or its French cousin Comté), havarti, or young Italian and French cheeses like young Fontina, Tallegio, or Brie are great options.
The three usual optional add-ons are, thinly sliced tomato, very crisp bacon, or fine chopped tuna salad for a tuna melt.

Butter the outside of the bread, not the pan, and cover the whole slice. You can also use mayonnaise instead on the outside of the sandwich, this is a standard restaurant trick.

By the way, don't forget an assortment of great pickles and olives.

It occurred to me that if you are planning to cook them all yourself, more or less all at once, you might want to know about this method: Start trays of sandwiches in the oven, open-faced, then finish in a skillet. You'll get ooey, gooey cheese all the way through, plus nice and crispy toast.
so dont toast the bread first just put bread and cheese in oven first then on the grills.