remove plugs, valve covers, and turn over by hand only....
get a timing tape to fit your harmonic balancer, or make marks every 90* using the factory TDC mark on the balancer a reference, this will tell you when each cyl is up to firing position
#1 is the front cylinder on the drivers side of the engine....firing order is 18436572.
by turning the harmonic balancer bolt get #1 on firing position...as you turn the engine over by hand, clockwise from the front, notice what the two valves on #1 are doing, and watch your timing mark for #1 cyl TDC...the valve will open/close as follows...intake valve opening as the piston travels down the cyl (Intake cycle of the 4 cycles), intake closing when the piston starts up the cylinder, both valves closed when at TDC firing position (compression cycle), both valves closed as piston travels down the cylilnder (Power cycle) exhaust valve opens when piston starts up the cylinder (exhaust cycle)...the piston starts up the cylinder and as it gets to TDC exhaust valve will be closing and the intake will be opening....DO NOT adjust valves when the piston is at TDC here...you are 180* away from the firing TDC....watch the valves closely for movement and if you see no movement for about 90* before TDC you are on compression stroke to set the valves. you can also watch the distributor to confirm you are at firing position for that cylinder.
Now, when you get each piston at firing TDC position, (as you go through the firing order, the next cylinder to be adjusted will be 90* from the last when checking the marks you made on the balancer turning clockwise from the front of engine....confirm position by watching the rotor on the dist as well.....then adjust each pair of valves for that cylinder...
loosen both rocker arms for the cylinder you are working on, then tighten slowly by moving the pushrod up and down from the lifter to the pushrod, when the up and down movement is gone, go 1/4 to 1/2 turn further to set preload for a hydraulic lifter....if mechanical, this is when you check with a feeler guage between the rocker tip and the valve tip for specified clearance.
Continue through the firing order until you get back to #1 firing again, button it up and fire away
), but this is different from what the 88 factory service manual says. Maybe it's just a difference between the different years? I don't even know what year we're talking about with wilpetty's Blazer. I don't have it in front of me, but it only had two adjustment positions- TDC for cyl#1, and TDC for cyl#6 (which will be the time that the timing mark is showing TDC but cyl#1 actually isn't there). It then listed which valves can be adjusted each time. 
