Freshly fried tortillas are key to standout nachos.
If you're frying tortilla chips at home, sprinkle them with salt just as they come out of the hot oil. The salt will then stick to the chips more readily.
Use evaporated milk and cornstarch to create smooth nacho cheese sauce that will stay emulsified, even at room temperature.
For Smooth, Stable Cheese Sauces, Cornstarch and Evaporated Milk Are Your Friends
If you're assembling individual nachos, add the toppings at the last minute. This ensures that everyone will get the hot-bottom, cold-top experience.