From looking at a cam I've come up with an easy technique to guarantee you are setting the clearance on the cam opposite the lobe. Turn the engine until a valve depresses. Then, set its 'mirror image'. Like this:
#1 is down, set #8
#2 is down, set #7
#3, #6
#4, #5
#5, #4
#6, #3
#7, #2
#8, #1
To make sure I don't miss anything I just pull the coil wire and just crank until the next valve in the numeric sequence goes down and just set them 1 through 8. This only works out so simply due to the firing order and mirror imaging of the ports.

How often you set them depends on how you drive the engine, among other things. From my experience a hard driven engine will recede the valves at a slightly faster rate, and you'll need to set them more often before the receded valve takes up all the slack and starts to hang open slightly - it will burn fairly rapidly. I set mine about every 5000 miles, but I rev mine pretty exuberantly.

Don't tighten those lock nuts too tightly or you will break the adjuster bolt - as I have done before. Snugly and firmly, but not tight.