Valves need to be set regularly, and more frequently right after head or engine rebuild. Once stable I'd say every 10k - 20k miles. Really helps to get steady running engine and balance the load on the cylinders. Essential for tic-tic-tic Swiss-watch-even idle (my ever elusive goal).
Read up in the FSM. Also search here. I've written my preferred tricks several times. Good post above w/ first time cold recommendation. Once you get the hang of it and valves are not too far off, it's easier to do hot per FSM recommendation.
I think the special open end 17mm wrench from MSA or Snap-on really helps, although others do get by with normal 17mm wrench. Some say to take all the rocker clip springs off, but I don't bother. I just check that they're all in place on button-up time.