Developing good serves involves watching players with good serves, getting good coaching, and lots and lots of practice. But sometimes, after all that practice, it's hard to execute the serves in a game as you do in practice. There's a simple reason for that - pressure. There's no pressure when practicing serves, while in a real match there is. It's especially difficult to serve fast & deep under pressure (where players often either miss or slow them down for safety, thereby lowering their effectiveness), in controlling the depth (where that "perfect" half-long serve - where the second bounce would be right on the end-line, now goes long and gets looped), and serving very low to the net. How to overcome this?
Easy - put pressure on yourself! After you've practiced your serves to the point where they are near where you want them, imagine you are playing real games. Imagine an opponent. Really get into the mind-set, and soon you'll feel the same pressure. Then you can practice serving under that pressure. Make sure that, under this pressure, you can still control the speed and consistency of the deep serves, and the depth of the half-long serves (second bounce right about the end-line), and the height of all serves. Most players tend to serve a little longer under pressure, and so their short serves suddenly get looped.
You might also add to the practice by putting targets on the table, to work on your accuracy under pressure. Put a bottle on the corners and practice hitting them with your deep serves at "deuce," or even "down match point."
If you can't execute your best serves under the pressure of a match, then you haven't mastered those serves, no matter how well you do them in practice. So . . . master them!