When I built my wheel myself (my first wheel) I didn't want to spring for a tension meter. A friend who has done a fair amount of amateur wrenching said "just really lean into the rim then torque them down until you think you're almost ready to strip something."

I did that - got the spokes basically as tight as I could with my little hand spoke wrench and home-made from 2x4s truing stand. I equalized the tension by plucking the spokes and getting the pitch about the same, then trued.

In the 16,000 miles I rode that wheel, it never even went a millimeter out of true. Dead straight and no problems from the moment I put it on the bike.