The reads
Guides.
The longer pieces. Cornerstone reads on the topics every finisher comes back to.

Start here
The complete sandpaper grit chart
Every grit from 40 to 3000, what each one actually removes, and the order to run them in. The one guide to read before any of the others.
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Guide
What grit sandpaper for woodworking?
The full grit sequence from raw lumber to final finish — by wood type and by task.

Guide
What grit sandpaper for auto body work?
Filler to final polish, 80 through 3000 — wet vs. dry, DA vs. block.

Guide
How to wet sand: the complete technique guide
First stroke to final polish — paper, lubricants, reading the slurry, by application.
Also on UltraRough
3D print sanding guides →
Layer lines, threads, and finishing — a separate section for printed parts.