I just ride a lot and make incremental adjustments over 500 - 600 miles (1 month for me). I start with a baseline that works for me. I have a good sense of body position and can feel very small changes pretty easily. I know what's comfortable, and dial it in by over and undershooting movements until it's just right. It's iterative because i'm working height, set back, and tilt. A change in one may necessitate a change in another. When i can't improve it anymore, it';s done. This is starting from a perfectly acceptable baseline position, which I do not measure. I'll usually keep a change for at least 50 miles (2 days or so), unless it's obviously bad.