I lay all of my spokes on the bench and make sure they are the same length, not bent, etc. From there it's simple geometry. If all spokes are the same lenth and tightened the same amount, the rim will be pretty darn close. So, I mark each spoke with a sharpie one inch from the end with the threads. Then, you just tighten the spokes a very little bit at a time, judging your progress against your marks, until they start to become snug and there is no slop in the rim. Then I mount the wheel and use a dial indicator to finish it off. Take your time and tighten each spoke a very little bit at a time; constantly using your marks on the spokes for reference. And, this is important, put a little grease in each nipple for anti-sieze.