Here's some tips. When the rudder is down -

1. The top part should be as far forward in the rudder box as possible - so it's as close to the pintles as you can get it.
2. The leading edge at the tip (bottom end) should be 5 to 15 mm in front of the centreline of the pintles - you can judge this by eye just by looking down the line of the pintles.

Both rudders should be set up identically.

The head of the rudder blade should be a snug fit in the box when it is down. It needs to be held solid in the box over the whole area of the box - not just at a point.

Of course, after you've done all that, the two rudders must be parallel to each other, and vertical (in line with the centreboards). It's no small task setting up rudders.