Pretty good use of your body and good arm (pronation) movement.
You have some good advice above already. But adding in the greater shoulder rotation will take a long time to get the timing down.
What I would recommend you working on first is the following:
1. Get a more agressive shoulder angle by getting your tossing arm up straighter.
In pic 1, Pete has his shoulder angle so steep that his tossing shoulder is straight up, and his hitting shoulder is straight down.
[Note that over the hitting his sequence in pic 10, he will end up with his hitting shoulder straight up, and his tossing shoulder is straight down. That reversal takes his arm through a longer distance, giving more time to build up speed.]
2. Don't drop your tossing arm too soon - it looks like you are letting your tossing arm drift down too early.
If you let your tossing arm start to drift down to early, you will lose that steep shoulder angle I recommend above.
Look how long Pete's tossing arm stays straight up in the above photos from pic 3- pic 9 while he is increasing his knee bend and forming more of a bow shape to get into his optimum trophy position to exlplode from.
3. Get a little more lean back of the upper body. See pics 3-9 above. As you have your tossing arm up and are then bending your knees and getting into more of a bow shape, bend back FROM THE KNEES WITH YOUR HEELS OFF THE COURT (not by arching your back) to get more of the lean back you see Pete gets by pic 9 in his trophy position.
[This will not only help your swing, but help prevent a shoulder injury from opening up the shoulder angle, with less impingement on the most superior of the rotator cuff tendons (supraspinatus).]
As you do this, you will notice you've got to change the angle of your racquet so it appears that you are not hitting with as straight an arm through racquet angle as you currently do.
But that means you will have a better pronation movement - with the increased power that a more powerful pronation will give you.
You can see this appearance of the racquet looking at more of an angle to the hand at ball impact in pic 19 above. But notice in the preceeding pics how the racquet/arm can be pronated through a greater distance for more power, plus the greater low to high motion for more spin.
4. "You've got to drop the left shoulder" - Jim McLennan
In this video, Jim emphasizes that getting great shoulder over shoulder action is good for your shoulder - there is no pinching of the rotator cuff.
But this is also the way to fully utilize your upper body movement for maximal power and spin.
Look at that first sequence of the Sampras serve above. In pic 1 his tossing shoulder is straight up and his hitting shoulder is straight down.
His shoulder angle totally reverses in the next sequences, so that at ball strike (pic 7) his hitting shoulder is straight up and his tossing shoulder is straight down.
Again, I think you can incorporate all these tips fairly easily into your current already pretty good serve.
After incorporating these, I think you THEN can go on to incorporating the big shoulder turn that will get you even more power.
But as you can see from the above sequence where Pete ends up with his back
facing the court that this needs to start during the ball toss, and I think for most this harder to add in than the above, even though it should eventually be your goal.