For someone new to the game he gets into a nice "bow' shape, and gets and keeps his tossing arm high.
I see two major areas for improvement:
1. greater shoulder turn
2. deeper racquet drop, then aiming the butt of the racquet at the ball as the elbow is extended until the late pronation movement
In the above sequence, notice how Sampras rotates/coils his shoulders/upper body/hips left to right away from the ball. This starts as the tossing arm is being raised, and the coiling continues after the ball is released. Bending the knees is essential to continue coiling completely.
Here is what coiling looks like from above:
Notice he starts with his shoulders perpendicular to the opposing court, but as the ball is being tossed, and after release as the ball is still rising, he coils his shoulders/upper body/hips to a position where the shoulders orientation is almost parallel to the baseline.
Powerful uncoiling is one of the major power sources in the serve, as emphasized in this video:
Roddick 150 mph Serve Analysis
http://www.youtube.com/watch?v=pLf_MJXzBVg
The other area for improvement would come from a deeper racquet drop and then acceleration of the racquet but aimed up at the ball to get maximum elbow extention before the late "snapping action" of pronation.
In the above sequence of Sampras, you can see how deep his racquet drop is at pic 4. The racquet butt is aimed straight up at the ball, just like you would do on a forehand. The next frame (5) shows how the initial motion is almost straight up still aiming the racquet butt at the ball. This "pulling" the racquet almost straight up insures you will be aiming "up the mouintain" with your swing. By photo 6 he is still largely aiming the butt of the racquet at the ball, but has begun into his powerful pronation movement.
[The reason I am emphasizing this aiming the racquet butt up and at the ball and pulling the butt up as the first movement in the forward swing is that your friend seems to be bringing the racquet
forward as his initial movement, insuring he will never get full upward racquet extension.]
To work on a more powerful pronation movement, have your friend try this drill, and then incorporate the more powerful pronation movement into his stroke for that last added burst of explosive power/spin.
McCraw explaining a serve pronation exercise:
http://www.youtube.com/watch?v=iONY6fcqZGg
Watching the player in the following video, specifically looking for the points mentioned above (coil/uncoil, deep racquet drop, aiming the butt of the racquet at the ball in the initial upward pull, and a powerful final pronation movement) may help convince your friend that with practice you don't have to be a tour pro to have sound technique:
Sarah practicing serve.She is 8 years old.
http://www.youtube.com/watch?v=iONY6fcqZGg
Although admittedly, a pro like Fed will do it even better:
Roger Federer - Super Slow Motion Flat Serve
http://www.youtube.com/watch?v=InYd8IrFnkU&feature=related
Good luck!