To set the rockers, start out by turning the engine over with a large ratchet and socket that fits on the bolt that holds the balancer on the crank. I leave the spark plugs out and all the rockers off when I do this. Watch the pushrods as you turn the engine, making sure that they go up and down on the cylinder that you are working on. If they don't, they aren't located in the lifter. Correct that. The two pushrods will move one after the other as you have the exhaust, then the intake lobe on the cam go by. After the second (intake) pushrod comes back down, go a bit farther (not enough to start moving the exhaust pushrod again) and stop. Now you can install the rocker arms and torque them to the 20 ft.lbs for stock locking nuts. If you have the poly-locks, tighten the nut as you turn the pushrod with your other hand. When you feel the pushrod stop turning freely, give the nut an additional 1/2 turn and lock it down. This will give you enough preload in the lifter to get things going. Continue to do each cylinder. When you are done, double-check each rocker nut to make sure it is locked and replace the valve covers.
If you want to readjust the rockers after starting and warming up the engine, buy a set of "piddle clips" to clip on the pushrod end of the rockers to avoid spraying oil around, remove the valve covers and install the clips. Restart the engine and, one at a time, go down the row of rockers, slowly loosening off the adjusting nut until you hear the clicking of excess lash. Tighten until the sounds just stops, then add 1/8 to 1/4 turn and lock. This will give the least amount of lifter pumpup at high revs.