If you are adjusting with the engine off, you need to loosen off the rockers until the pushrod spins freely between your fingers with very little effort. Tighten the rocker until the pushrod no longer spins easily but no more than that. That is zero lash. You can loosen and tighten the rocker a couple of times to make sure that you are actually at zero lash (I had to reset the valve lash for one fellow who had tightened the rockers down so far he completely bottomed the lifters to get the pushrod to "stop turning", then added more! The engine didn't run very well!).

From zero lash, add 1/2 to 3/4 turns. If the lifter is a slow bleeder, the valve will open as you turn down the nut. Don't worry about that, that's normal and the lifter will settle into proper operation when you start the car. Other lifters may bleed more quickly. Again, don't worry; as long as you are setting from zero lash the lifters should work correctly when the engine is running.

Start the engine and let it run for a few minutes to get the lifters bleed down or pumped up as needed. If the engine isn't running well and you still hear ticking, set the valves with the engine running. It can be messy but you'll get to hear the difference as the lifter adjusts to the preload. They should take about the same time to adjust. If you have one that adjusts very quickly it may be faulty.

If you really do have valves hanging open you'll see the fluctuation in the vacuum.