All of the above recommendations to improve your serve are good ones.
But I sense you are seeking to get a proper rhythm in your swing that will feel comfortable, and allow for consistent serve after consistent serve.
Perhaps the following advice I recently gave another will help:
"The reason most want a higher ball toss is that they seem rushed and run out of time
getting into their trophy pose and then getting all the way through the racquet drop/hitting sequence.
To get more time...
Don't toss, THEN start to get into a trophy position.
Instead toss AND start getting into a trophy position
... at the same time.
Go back and look at the video that Systemic Anomaly posted:
Federer Murray Haas & more ball toss common threads http://www.youtube.com/watch?v=lIF-UaRUd6k
The whole point of it is that all the pros are rotating their shoulders back to coil at the same time their tossing arm is going up.
[And to coil and remain balanced, you also have to be bending your knees at the same time!]
Check out the sequence of Sampras tossing below:
In pic 1, with the ball very low down near his knees in his tossing hand, the line of his shoulders is almost perpendicular to the service box he will serve into [not totally perpendicular as his front foot is to the right of his left foot].
But as he brings his tossing arm up (pics 2-5) by the time of ball release (pic 5) his shoulders are significantly coiled. [Although he continues to coil even more soon after ball release in pics 6-8.]
Tip #2: Don't "arm" your ball toss!
We've all been told not to "arm" our groundstrokes and serves.
Instead, the hitting arm motion should be preceded by a big body motion (coiling), to generate the initial energy in hitting the ball, with the arm swing following the reversal of the big body motion (coiling to uncoiling).
So too on the toss, a big body motion to initiate momemtum followed by a reverse of the big body movement, helps get the arm going up. But in the case of the toss, the motion is not coiling, but instead first leaning into the court, then leaning back, to helps get the arm going up!
Go back to that video of all the pros serve tosses. Note that all first lean into the court, then lean back.
Federer's lean in and lean back is more exagerated than most, but as usual, Fed is not wasting motion here:
When leaning in (pics 1,2 above), the tossing arm is going to going to be very low.
When leaning back, the tossing arm is going to start to rise as the shoulders and hips go from a downward slant (pic 1 above) to no slant of the shoulders/hips (pic 2) to an upward slant (pic 3).
This reversal of the shoulders/hip from a downward to upward slant provides the momentum to get your tossing arm moving upward.
The result is that you don't have to work hard on your toss if you let your big body movement help supply the energy.
[To those who have already noticed this "lean in" is actually "forming a bow shape" forwards, with the 'lean back" going all the way past vertical to forming the "bow shape in the opposite direction in the trophy pose - see tip #4 below - only to reverse again through the hitting motion.]
Watching the video helps to emphasize the "lean in" and "lean back", and how the toss is intrinsically interwoven with getting into the trophy position:
Roger Federer - Serve in Slow Motion http://www.youtube.com/watch?v=D4PfHpKbJSI
Tip #3: The tempo of how fast you lean back, from your initial lean in, determines how fast to elevate your tossing arm.
Every orchestra needs a conductor, and every conductor has a baton to set the tempo of the music.
Your tossing arm is should be going up at a constant speed, and your tossing arm acts as the baton to set the tempo to your serve.
Tennis Serve Tossing Motion Tempo http://www.youtube.com/watch?v=CeZp9...feature=relmfu
How fast your tossing arm movement should move comes from how fast you lean back (pic 1 to pic 2 above) in the initiation of the toss.
[Lean back too fast, and your tossing arm will move up too fast, and the ball will go too high.
Lean back too slow and your tossing arm will move up too slow, and ball will not be tossed high enough.
Lean back "just right" and your tossing arm will move up at "just the right" speed to get your toss to the right height.]
Tip #4: Your tossing arm continuing up and up and up until it is straight overhead gets you into the bow position.
Getting your body into the shape of a "bow" (when viewed from the side), is something everyone agrees is important to get that big shoulder over shoulder cartwheel action that can help power your serve.
As your tossing arm continues to go up after the toss (pics 3-4), you will automatically be getting a steeper shoulder angle.
With that steeper shoulder angle, your front hip will have to protrude over the baseline (pic 5) to counterweight the backward lean of the upper body to the fence.
This is what Brent Abel is emphasizing that video above where he states that even after ball release, your tossing arm should continue up, up, up at a constant rate, and allow your left hip to protrude forward.
Your "toss" should be perceived as being set up by a big body motion (lean in) to get it started.
The "toss" also should have a "follow through" of your tossing arm going up straight overhead to get you into the agressive trophy position you'll need to bash that ball."