So you don't get screwed up while adjusting, it's a good idea to mark each rocker after you adjust it...I use a black marker pen on my light colored rockers but you can also use a small piece of tape put on top of each rocker after you finish adjusting it..This way you don't miss any or redo any by mistake.........WW

 

all right I'm chiming in.
I have read so much on this it made my head spin as much as the push rod.
This was my answer.
first follow any of the above mentioned methods to get yourself in the ball park.
second get yourself some cardboard to shape along the bottom of your head with the valve cover off ( splash shield )
Make sure you have had the engine heat soaked prior to staring adjustments
pull one cover. Start the engine back adjustment nut off on one valve until it ticks then tighten until tick stops from there go 1/4 turn further. repeat on all valves on that bank.
repeat on other bank. If the car becomes hard to start you are to tight.
The reason behind this method is 1 not all lifters will have exact oil flow and therefor will pump up differently. Lifters will not Pump down completely after sitting for awhile but will drain off slightly again at different rates. If you want to use the feeler gauge method take a small pick that will fit down the center of the lifter and push on the check valve several times until you can depress the center of the lifter all the way down ( pump down or empty the lifter)
It is the most accurate way of making sure all lifters are in the same state. Just remember at that point when you adjust you will be pushing the rod to the bottom of the lifter and should have serious gap between rocker and valve. so if you have 1.5 rockers and want .030 pump up on the lifter you need a .045 feeler gauge fitting snug between rocker and valve this is a dry valve method but the .030 as stated above can not be used as a one size fits all measurement as your oil pressure will have a direct effect on how much the lifter will pump up.
At least using the engine running method you will be adjusting the lifters it the state they will be operating in.

 

careful about over tightening...its not that hard to wipe out a cam lobe.

 

very true do not over tighten but if you get the first one I have found you can pretty much look at the threads on that one and use it for a starting point for the rest.