Having just recently replaced the cable on my steering system this is what I did.
1) Visually align the rudder to be straight. I can see the rudder from outside of the boat and was able to align it to centerline visually. N.B. this is a physical alignment which may or may not cause the boat to go straight.
2) adjust the rudder position sender to indicate straight. This lets the AP know where the center of the rudders travel is. Assumes that the travel is equal both sides of center.
3) With the steering wheel in the "straight" position I placed the center of the steering cable drive chain on the top center tooth of the steering shaft sprocket. This centers the steering cable
4) tightened the steering cables on the quadrant equally (port and stb cable) until I got the tension I wanted in the steering cable.
Poof - statically aligned steering.
I did end up tightening the steering cables a bit more because the (backup for below
deck AP) wheel pilot dithered a bunch due to the play in the steering cables.
Also, when motoring or sailing the various side forces (prop torque, differences in port to stb
hull shapes as heeled etc) will cause the boat to need a bit of
helm to go straight. No surprise there.
Regards