I start by snugging up the upper two shrouds then raising a 100' tape to the mast head and measuring from side to side and adjusting until they are exactly the same. Then I tighten each the same number of turns; 5 port/5 stb until I've got the about the right tension on them. The intermediates and lowers I do by sighting up the mast making sure it is straight. I tend to err on the side of being too loose, then adjusting after observing the rig during a sail. I've found that none need be bow string tight.
SV Laurie Anne
1988 Brewer 40 Pilothouse