Ok, here is the technique up to 800 grit. 1000+ to follow along with some vids.
(This is for natural finished wood - does not apply to a thinly veneered guitar....)
1. Sand wood to 320 grit. Depending on the marks to remove I go through 80,100,120,180,240,320
As per DB's mantra spend a lot of time on this getting it right. Your arms should REALLY ache after each grade of grit....
2. Apply liberal amounts of Tru Oil to the wood. Let it sit for 10 mins or so, letting it really soak in. Then, rub it off with a cloth (I use a pad of worn lint free cotton t-shirt). When I say rub it off, really hit it hard like you are polishing it, across the grain and with the grain). If you've done this correctly your pad will travel smoothly over the wood and there will be little to no Tru Oil visible on the surface (but it has rubbed into the grain and will seal it)
3. Progressively wet sand the wood with Tru Oil. Starting on 400, then 600 & 800 grit. Leave at least 24 hrs or more between sessions. Load up your wet/dry paper with Tru Oil and sand with the grain. You'll feel when it is cutting the previous surface (there is some friction) and when you've sanded enough (the sand paper will glide over). Work in small sections. Load up paper with Tru Oil as needed (don't let it get dry but don't overload)
After each wet sand, take a fresh cotton pad and wipe the Tru Oil off. I found pushing the pad away from my body along the length of the guitar works best for initial wipe over. Then around the edges to catch any drips. Lastly rub and burnish until it feels like your arm is about to drop off! If the pad starts to stick (you'll know what I mean) add a bit of mineral turps to the pad for lube.
If you've done this correctly (up to 800 grit) it should look like my previously posted video.
My previous Tru Oil efforts resulted in way too much build up but so far the finish achieved with this technique is to my personal liking
More to follow...