Depends on what you are referring to. If you have a one piece driveshaft, it should be "right" so far as rotational alignment, BUT SOME ARE NOT. That is, they were welded up by someone not paying attention
So, you take the one piece shaft and sight down it just like a rifle. The caps on each end should be aligned perfectly.
The other side of the coin, is installation of the shaft into the rear yoke. In theory they should be balanced, but the fact is that if you run it, and rotate it 1/2 turn at the rear, it "might" run smoother
The easy answer on pinion angle, is that with the car on it's suspension, loaded normally, and under med--hard acceleration, the transmission shaft should be parallel to the pinion shaft.
