Assuming you have adjustable rocker arms or adjustable pushrods.
Tighten until there is zero slack in the rocker to pushrod and then turn another 1/4 to half turn.
IF you are using the stock rockers and stock pushrods, then you are stuck with what you have unless you can get rocker shaft shims. This would move the rockers away from the valve tip and pushrod giving you less preload. OR order custom length push rods to give you the preload you want.
I assume you know about leaving the lifters sitting in oil over night to get all the air out of the lifter plungers. IF not, you will never get the prelaod right.