From what I can tell there are just a few important things to know:
1) Achieve perfect hard-boiled eggs: place them in a pan of tap water, put a lid on, let it reach a hard boil, and then take them off the heat. Ten minutes later, you'll have hard-boiled eggs.
2) Slice your eggs, don't mash them. Ideally, slice them in an egg slicer, criss-crossed two or three times until you've got cubes or at least slender slivers.
3) Figure about 2 Tbsp of mayonnaise for every 3 eggs. This particular combination makes enough for two sandwiches, as far as I'm concerned. Adjust accordingly.
4) If you've got them, toss in a spoonful of dijon mustard and a tsp or so of lemon juice.
5) Salt and pepper are essential here - if you leave them out, the whole thing tastes boring.
6) Adjust as you see fit: I like to add green olives or sliced red pepper. This cookbook suggests a more standard mixture of celery, parsley, and red onion.