Get the mast standing straight, use the halyard to measure distance to port and starboard chainplates. They should be the same. Tighten until it feels tight when you pull against it. Assuming you've set your rake and backstay tension properly, take her for a sail, a nice beam reach in somewhere around 15 knots of wind. Watch the leeward turnbuckles. If they go slack, tighten both sides equally just until they don't go slack. Set the sails you wish to sail with and follow the same procedure. Use your eye to sight up the main track to check for any bowing under sail. Tighten the lowers until the bow is minimal. Remember, what you do to one side, do the same to the other.
-Will (Dragonfly)