vs CPU serve tips
If you're looking for an easy time against the CPU there's a way to serve that'll almost guarantee a pass everytime.
Juergen - When serving, take two and a half steps to the right. One step is considered as Juergen's left foot crossing his right; do that twice and then another half step right (just tap the left analog). Tap X to set Juergen to serve. Press and hold left on the left analog stick, then press and hold X to power up a leftserve. While continuing to hold left on the analog release X when the white (spin bar) bar is full and the black (power) box is at 85%-100%. Your serve should slice, hitting your side of the table, jumping over the net, touching the inner-left part of your opponent's table and droping out of reach, everytime. If you fault then you took too many steps right.
Kumi - Same method, only with Kumi take three steps right. One step is Kumi lifting her right leg and setting it down. You will not be as far out as with Juergen because Kumi has less power. Everything else is the same, the holding of the left analog, the use of the X button and the spin/power levels. Again, first hop on your table, next hop on your opponent's far left side and out, untouched.
General Play against CPU
For the Amateur and Rookie levels you can simply use Jesper and be "A button, smash happy" all the live long day. But the Pro and All-star levels require a level of patience and mostly defensive play; you must pick your spots.
And for that is answer is simple...
...backspin (Y button), all day, everyday.
The backspin will force the CPU to return a similar backspin shot or a different shot of less power. Continue to backspin until your focus bar is full, then once the room darkens (a sign that your focus bar is full) feel free to use the topspin (A button) for some slams. If you fail to put your opponent off balance go back to the backspin, wash, rinse, repeat. And with the backspin the CPU will often make mistakes (a shot out or a net), sometimes three or four a match, but you'll have to play rallies of 50-200 before you see that on the All-star level.
It should be common sense at this point that you should be holding down the Y button immediately after you make a shot; that means you're holding it as the ball is sailing towards the CPU and while they make their shot.
More character positioning will be added as I progress through the "finish all-star with all characters achievement".
Hope this helps everyone.