Here is the optimal start to a serve.
1) continental grip with the wrist tilted up towards you
2) full body weight is on the left leg (for a righty)
3) both hands are on the racket (gives right hand rest because left one basically hold the entire weight of the racket)
4) shoulders are fully turned sideways
5) back foot is behind and to the left of the front foot (securing the ability to coil later on)
Here are a few more examples.
Shifting the weight from the front foot to the back one.
1) both hands are still on the racket although they start disconnecting
2) shoulders stay turned
3) front toe frequently gets of the ground
More examples. (it was hard to find good pictures of this phase, but if you slo-mo any high-level serve, you will be able to clearly see that it is in fact there)
Toss and body shift inside the court
1) racket angle remains the same as the beginning
2) tossing arm stays straight throughout the toss motion
More examples of this.
1) feet can come together or stay in the same distance they were in the beginning. Both equally correct
2) racket face is still tilted in the same angle it was in the very beginning
3) elbow is off the body
4) tossing shoulder all the way up, hitting shoulder all the way down.
5) tossing arm all the way vertical
6) hips inside the court, creating C shape
7) shoulders turn further away from the court, the opponent should see some of your back
8) knees bent
9) rackets stands up vertically
More examples of this phase.
1) racket drops all the way down behind the back
2) tossing arm gets out of the way
3) rackets still angled, like you are trying to hit the ball with your frame
Here are the different angles of this phase:
Here are more examples: