[Ol'Jim]

WAIT!! Firing order on GM V-8's is 1-8-4-3-6-5-7-2.
With all due respect, DO NOT follow the advice in the post just above this one! At least not the part about adjusting them in pairs. The cylinder pairs listed are both at Top Dead Center (TDC) at the same time. What that means, is while Cyl #1 is at TDC on the Compression (firing) stroke, with both valves closed, in perfect position for adjusting both valves, Cyl # 6 is also at TDC, but it is during the transition (overlap) period from Exhaust stroke to Intake stroke, meaning BOTH VALVES of Cyl #6 are partially OPEN, and CAN NOT be adjusted!
I do agree with the advice from same guy about not tightening Hydraulic lifters beyond 1/2 turn max, (after achieveing zero lash), I stay at 1/4 turn, with new OR used parts. Less chance for lifter pump-up to cause valve float at higher RPM's. NEVER exceed 1 full turn, which will bottom-out most hyd lifters!
Here is where you will find the advice you asked about - (And NOTE, there is NO procedure that lets you adjust a full side at a time - NOT possible). Go buy a copy of How to Rebuild your Small-Block Chevy, by David Vizard. It is either an HP Books publication, or a Peterson Pubs book. Available at most large parts stores, (Advance, Autozone, O'Reilly, etc), or from Amazon.com, where you can get used copies for a couple $. GREAT book for all SBC people. It will give you the procedure on how to adjust all 16 valves using only 2 crankshaft positions, which does save time. Some Cyl's you can adjust both Int & Exh at same time, but most are doing the Int at one crank position, and the Exh at the other position. I don't recommend adjusting while running, oil splatters everywhere, even with those worthless clips you can buy.
Option #2, more time-consuming, but nothing is more accurate: The EO/IC method. (Exhaust Open/Intake Closed). Engine builders do it this way in every major form of racing. You do one cylinder at a time. Remove all sparkplugs for ease of turning engine. If you can get a breaker bar & socket on crank snout, I recommend that method of turning engine, but you can bump the starter instead.
For each cylinder, turn the engine until the Exhaust rocker/valve just begins to Open. (EO). At this point, you adjust the INTAKE valve for that Cyl. Then rotate until the Intake valve you just adjusted opens, keep going until it just closes. (Intake Closed = IC, now you understand EO/IC). When it has closed completely, now you adjust the EXHAUST valve for same Cyl. Proceed to next Cyl. You can do them in firing order, or by one side then the other, or in ANY order you like, just do both valves for each cyl sequentially.
As for how to adjust the valves, when you get the crank positioned for a given valve, back off the rocker nut about 1-2 turns to loosen that valve, then slowly tighten it with a ratchet, while your other hand rotates the pushrod between thumb & forefinger. Just twist it back & forth, that pushrod will spin easily until the lash approaches zero, and it will snug up and get tighter, and harder to rotate. At that point, you've removed all the slack, (lash), and so now you just need to pre-load the hydraulic lifter by tightening the rocker nut 1/4 turn more. Stop, you are done. Move on to next valve. For solid lifters, you would not pre-load, but instead of the pushrod twist, you'd have the proper feeler gauge in between the rocker & valve stem. It is really simple, and once you do a couple of cylinders, it is an easy routine to follow. I highly recommend it, that is how I do them on new builds, and in-the-car.
Note: Once you have adjusted hydraulic lifters, there really should never be a need to adjust them again. Occasionally, a really old rocker nut may lose it's self-locking ability, and become a bit loose. But if one or more cam lobes ever wear enough to cause the lifter to lose it's pre-load and make noise, you have much more serious trouble than simply adjusting the rockers. They should stay quiet for well over 100,000 miles, as long as the oil is changed regularly. Good luck!