- Use very fresh eggs and good-quality pancetta, bacon, or guanciale -- there are such few ingredients in the dish that these need to shine.
- Lift your pasta straight from the cooking water and add it to the egg and cheese -- the starchy water is a key binding agent. Save the cooking water to add if the dish needs more moisture (it probably will). It is magic.
- Don't discard the bacon/pancetta/guanciale fat - use it in the sauce.
- Go heavy on the freshly ground black pepper.
- Your cheese should be freshly grated (pecorino, parmesan, or a combo).
- EAT IT STRAIGHT AWAY. Preferably with a glass of wine.
If you can mess up carbonara you should be led from the kitchen in handcuffs. Allow me to amplify on Bstar's good advice; remember to you do have to cook pancetta or guanciale first, but the hot pasta straight from the pot will cook the eggs sufficiently. Some people get wimpy on this last step. And please note that adding cream is a total cop out, although some people do that.