Primary shrouds and stays should be tensioned to 15 to 20% of their rated breaking strength. To tension the shrouds properly you will want to buy a Loos gauge. If you tap the shroud with a hard object there should be an audible dull ring. Before everyone jumps on this and responds with "that's way too tight"; I'll point out that I am relaying the advice of Brion Toss.
In addition you might want to do some rig tuning; check out the thread that is stickied to the top of this forum about adjusting your rig.