Remember to be patient, young grasshopper.
I built one wheelset a long time ago, and have re-built a couple of wheels in the last year. It seems that everything seems to go well until about halfway through the truing process when I seem to get completely confused and start turning the wheel into a slight taco.
After a day or two, I come back, untighten all the spokes, then taking my time begin to re-tension them and slowly true the wheel.
So far my wheels have given me good service, yours should too.
Good luck!