<a href=http://dimequarterly.tierranet.com/tech/valves.html>here</a> is a great writeup from a 510 site. The Z engines are basically the same only with an extra 2 cylinders worth of valves to adjust.
Definitely do it cold your first try. Many people say it's more accurate to do it hot, but if a lot of the valves are off and you're still getting the hang of it you'll take too long. The car will cool down as you work on it and the measurements won't be accurate. Let it cool down overnight.
There's a couple of different ways to turn the engine to get at the individual valves. Some people like using the starter motor for this. (make sure your plug wires aren't connected and the car is in neutral!) Another method is to leave it in 4th or 5th gear and push the car a little. I put a socket wrench on the nut at the end of the crank and turn that.
One more tip.. rather than disconnecting the individual spark plug wires in order to remove the valve cover, just remove the middle wire on the distributor cap and pull the cap off and over to the other side. Quicker and less chance of pulling a wire out of its socket.
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.