I know there are many out there having trouble figuring this out, so I built this thread in my free time this evening. I know, my phone's camera wasn't the best choice.
We're going to start from the beginning:
First, we'll throw in the valve. This often requires a 'Cocker/Sniper valve tool, though some have gotten away with simply using a 1/4 allen key. Assemble the valve, spring and jam nut as shown:
Then cram them in there, like so. Thread the jam nut in most of the way so the valve opening appears as shown.
You may need to use another tool to line it up.
Next, collect your valve retainer and a 5/16 allen key and tighten it into place.
When it is tight, cinch the jam nut as well. It should look like this:
Next, locate your hammer and cocking rod. Threading them together will make the hammer much easier to index for the next step.
Slide your 1/8 allen key into the hole at the top of the body as shown, and wiggle the hammer a bit to seat your tool into the hammer lug.
3-4 turns in will usually do the trick, though it will depend on the frame and hammer you use. This is a good depth to start.
Next, grab your main spring and IVG and drop them in. Almost all IVGs have a "cupped" side that goes in first to hold the spring in place.
This is the farthest "out" the IVG can be for most guns. Roughly two threads.
At this point you'll want to install your pump kit. For those with secondary guide rods, I get them roughly hand tight at this angle and use a tool to cinch them up. Slide your handle into place and make sure the pump arm doesn't rub on the body.
Hopefully you haven't lost your backblock, bolt, bolt pin or cocking rod by this point! Add them, your trigger frame and other parts as desired. Make sure that you install your bolt with the hole downward.
If adding an autotrigger as seen here, you will likely need to tweak your hammer lug just a bit, but that's a demo for another thread!