Work for reproduction is very different than a one off piece. (Which, by the way, I don't enjoy doing at all.) I once did a huge family tree (twice) because I screwed up a name near to the end and I couldn't bear the thought of having a "fix up" on an original. I also didn't enjoy doing seating charts for the same reason.
In the past, I've done quite a number of one-off documents such as family trees and large ceremonial scrolls. I agree that this type of work causes a lot of tension which is counter-productive at the very time when you should be at your most relaxed to produce your best work.
Out of necessity, I've developed a few little techniques which help me....they may help others.
With large bodies of text, I use the computer to speed up and aid the layout. I write a line of text and scan it in. I then type the same letters below my writing, and with a computer font of similar letter proportions, I adjust the point size, inter-letter spacing etc., until it matches, more or less. I keep a note of this example for future reference. I then type all of the text and check it very carefully for any errors. When I come to write, I print off this block of text and cut it into line strips as a guide for my writing. I then lay each line in turn in position and copy down the word shapes with confidence. There is little chance of error, as I've already checked the wording for position, spacing and the text content itself.
I always do this work late at night when the phone won't ring and nobody will come to the door - in other words, no interruptions. I switch off the TV and often work in silence but I sometimes find that music has a relaxing effect. However, I avoid songs as the words can be disastrous. For example, If I'm writing the word 'for' and it coincides with the word 'from' in a song, it's very easy for me to write what I hear. I use soothing, instrumental music such as by Delius, Debussy or Ravel.
Coming fresh to a work session, I never start a large paragraph at the top. Using my lettering guide, I start at about 1/3 of the way down - say at line six for example. After a few lines of writing, I then go to the top and write in the first section.
The reason for this is simple. When the work is important, most of us experience some tension when starting to write, and this uncertainty is most obvious at the start of a body of work. By burying this uncertainty in the body of text, it is far less noticeable. I cannot claim credit for this tip, as it's been around for longer than I have.
Having to start over with a large writing project, and losing hours of work because of a relatively small error is depressing out of all proportion! Erica described it, and we've all been there! My routine helps me to mitigate against this unthinkable possibility. Above all, don't try to rush and don't cut corners!
Ken