When I was much younger, I adjusted valves with the engine running (that was how I was taught).
For the past 15 years,
I have been using this "static" procedure.
As stated in the instructions at the link above:
1. Make sure that each rocker arm surface that mates with the top of the valve stem is smooth. Grind smooth and polish, if necessary.
2. Warm up engine to a stable temperature and then run the engine for 30 minutes (this is important).
3. Stop the engine.
