1. Set engine to TDC #1.
2. Undo ALL rocker nuts until they can be turned by hand with a 15mm deep socket.
3. Remove pushrods and clean the crap out of them until they are no longer greasy on the outside. Reinstall.
4. With one hand on the pushrods for the closed valves (you will know which ones are open based on pushrod height), tighten down the nuts while pulling on the pushrods by hand in the up/down direction until the pushrod can no longer move vertically.
5. Tighten rocker nuts 1/4 turn more.
6. Turn engine over until #4 cylinder is at TDC (one crank revolution).
7. Tighten remaining nuts in the sequence described in step 4.
You're done!