Most players, when trying to serve fast and deep, are not really aware of where the first bounce is on their side of the table. Even those who are aware have a hard time seeing it as it happens rather fast. To maximize the speed, you want the ball to bounce as close to your end-line as possible - but most players, when doing this serve, have the first bounce well over the table, usually over a foot in. When asked, they often aren't sure of where the first bounce is, but assume it's close to their end-line, even if it wasn't even close to that. How to solve this problem?
Spread a towel on your side of the table, about six inches from your end-line. Then practice your fast, deep serves. Your first ones will likely hit the towel - instant feedback!!! Try serving so the ball hits in that first six inches. If you have trouble doing it, try hitting the side of the table on your end-line. Eventually you'll become more aware of where your first bounce is, and learn to keep it close to your end-line, maximizing the speed of the serve. Once you've done that, watch how deep your serve goes - now's the time to make sure it hits very deep, or once again you are not maximizing the speed. Once you've learned to serve so the first bounce is near your end-line, and the second bounce near the opponent's end-line, you can work on perfecting the serve, with various topspins, sidespins, and flat versions, to the wide corners and where the opponent’s middle would be. (It turns out Douglas Adams was right about towels!)
Here are some Tips on deep serves: