Alex, if I corrected the very few errors in this, it wouldn't sound like you anymore. Excellent advice, and it's good to know we tune essentially the same way, breaking it down into "at dock" and "underway" procedures.
I have 1/4" stays on the old, more race-oriented boat, and I swear since I learned about tuning I get a great deal more performance out of it, even though my back stay is fixed (no Navtec lever or wheel or ram).
A point here about tensioning: Don't bother trying to align your prop shaft and coupler until AFTER you have tuned the rig, at least at dock. I don't care for saildrives, but one advantage is that this problem of a tensioned rig "bending" the boat slightly is avoided. If you have the most common cutlass bearing and spade rudder set-up, align the coupler at launch just to motor to your dock and to the mast crane (if your mast is out). Tighten the stays just enough to keep the mast up, and then go back to the dock for a beer. If it's calm and you aren't drunk, follow Alex's fine instructions. Tune the rig at dock.
Leave the boat. Wait a couple of days. Come back and see if your prop shaft is still aligned. Maybe it isn't. Realign it now that the boat is bent according to the rig tension and not because it's been drooping off a cradle or jackstands all winter. You will probably find enough of a misalignment to make you glad you checked it out.