IDK if its the correct tech way,but I just tighten mine to were its hard to squueeze the spokes together,but they should still flex like 1-2 mm,if you squeeze them super hard..
While your tightening them,when they start to get tight constantly squish spokes together with a wrench,put the wheel on the floor and walk around on its sides,etc seats the spokes in and makes a much better wheel..should hear some nice pinging and popping noises..