With the motor off and the pushrod on the base of the cam lobe, tighten down the rocker arm with one hand while you are actively spinning the pushrod for that rocker arm in the other. When the pushrod gets to zero lash (you can't easily spin it anymore) go 1/4 turn further and you are done with that rocker, move onto the next one and rotate the crank accordingly to make sure each one is on the base of the cam when you do it.
2000 Mustang GT Steeda #0048
Just because I give you advice, doesn't mean I know more than you. Its just means I've done more stupid ****.