Well with mine I got my buddy to ride in front of me on a nice straight road and give me a wave when he hit 40MPH, then we both held our speeds the best we could and I pushed the needle down where it needed to be. Then I verified it by taking the leading and holding firm at 50MPH and his vehicle was also at 50MPH, viola. If nothing else, I'm pretty sure focushacks.com or myfordfocus.com has it mentioned in their how-to guides..
It is a pain in the butt, you just need patience. I did my gauges not too long ago, and had a batch of a time. I would get the speedo set and the tach, then I would turn the car off, fire up the test mode again, and it would be about 5-10mph off and 1k off on the tach. I'd align them again, turn off the car, fire up test mode again, and it would be off again. Man that was frustrating.