I have been building wheels in bicycle shops since 1975. There are several key elements which make a big difference in overcoming potential building problems, especially in dishing.
Dishing rear wheels is a PITA but can be reduced to a minor irritation if approached in the right fashion.
Assuming that you are dealing with a decent rim and the correct length of spokes, then the concept of centering the rear rim between the lock nuts (and not hub flanges) is the one thing to keep in mind throughout. Have I ever lost my concentration and moved the dish the wrong way...yes...it happens. Always put the wheel in the truing stand facing in same direction (I prefer the freewheel threads on the right when looking at it in the stand).
Here are some things you may find helpful.
The spoke threads, base of nipple heads, and rim spoke holes
must all be properly lubricated before lacing.
Begin by tightening the nipples gradually and consistently by using the visible threads remaining as markers. When they disappear, count the number of nipple turns. Later, you may see the spoke end thought the end of the nipple slot and use that as a reference. The object is for all spokes nipples to be threaded the same distance - initially.
Detecting when the spokes begin to lose their initial slackness and start to move the rim
is the point that makes all the difference in easier, accurate dishing, and removing/preventing rim "hop" (rim being out of round).
Spin the wheel and gun sight the rim in relation to the lock nuts and estimate where the rim will be properly dished. Using that reference, roughly true the wheel to that point using the least amount of tensioning as possible and then check the dish - the trueness does not need to be fine at this point as you are checking to see how close the dish is. It will be easy to make rim corrections at this point because of low spoke tension.
Once the wheel is close to being properly dished, then next adjust the hop without grossly affecting trueness. Then it is back and forth, keeping in mind that spokes on the right will be a lot tighter than the left side and the right side nipples will be harder to turn towards the end. As you are approaching optimum spoke tension, slightly over shooting the dish to the right (freewheel side) is a lot easier to correct than having it dished to far to the left.
Hope this helps!