I've found several of these guides/threads very helpful with my recent restoration.
**----** Playfield Area **----**
https://pinside.com/pinball/forum/topic/vids-guide-to-ultimate-playfield-restoration
https://pinside.com/pinball/forum/topic/cleaning-playfield-harnesses-vids-guide
https://pinside.com/pinball/forum/topic/cleaning-and-waxing-pinball-machines-vids-guide
https://pinside.com/pinball/forum/topic/vids-guide-to-upgradingrebuilding-flippers
https://pinside.com/pinball/forum/topic/the-spraymax-2k-auto-clear-in-a-can-club
https://pinside.com/pinball/forum/topic/pinside-rubber-ring-database-by-themetitle
https://pinside.com/pinball/forum/topic/vids-guide-fixing-stripped-screw-holes-in-wood
https://pinside.com/pinball/forum/topic/how-to-safely-flatten-warped-playfield-plastic
https://pinside.com/pinball/forum/topic/how-to-even-out-a-warped-plastic
https://pinside.com/pinball/forum/topic/vids-guide-re-populating-playfields
https://pinside.com/pinball/forum/topic/lexan-playfield-protector-install-and-review
https://pinside.com/pinball/forum/topic/vids-guide-to-rebuilding-pop-bumpers
https://pinside.com/pinball/forum/topic/making-new-ball-guides-from-scratch-vids-guide
https://pinside.com/pinball/forum/topic/replacing-stand-up-target-faces-vids-guide
https://pinside.com/pinball/forum/topic/say-goodbye-to-old-yellowed-plastics
https://pinside.com/pinball/forum/topic/removinglessening-yellowing-in-the-clear-areas-of-plastics
https://pinside.com/pinball/forum/topic/playfield-swap-guide
https://pinside.com/pinball/forum/topic/shop-job-master-checklist
https://pinside.com/pinball/forum/topic/ultrasonic-cleaners
**----** Cabinet Area **----**
https://pinside.com/pinball/forum/topic/cabinet-restoration-vids-guide
https://pinside.com/pinball/forum/topic/removing-side-rails-vids-guide
https://pinside.com/pinball/forum/topic/pinball-pimp-premium-cabinet-stencils-available-now-1
https://pinside.com/pinball/forum/topic/homebrew-webbing-step-by-step
https://pinside.com/pinball/forum/topic/pinballplatingcom-chrome-brass-black-nickel-powder-coating
https://pinside.com/pinball/forum/topic/powder-coating-services-offered
**----** Electronics **----**
https://pinside.com/pinball/forum/topic/replacing-line-cords-plugs-wall-sockets-vids-guide
https://pinside.com/pinball/forum/topic/vids-guide-quick-bally-driver-board-repair-bulletproofing
https://pinside.com/pinball/forum/topic/vids-guide-to-bulletproofing-williams-system-6
https://pinside.com/pinball/forum/topic/terrybs-soldering-guide-part-1
https://pinside.com/pinball/forum/topic/terrybs-guide-to-logic-probes
https://pinside.com/pinball/forum/topic/terrybs-guide-to-repairing-alkaline-battery-damage
https://pinside.com/pinball/forum/topic/stripping-battery-corrosion-with-a-strong-acid
**----** Aftermarket Parts Sources **----**
https://pinside.com/pinball/forum/topic/online-pinball-parts-shops
https://pinside.com/pinball/forum/topic/reproduction-bally-aprons
https://pinside.com/pinball/market/shops/1055-nvramweeblycom
https://pinside.com/pinball/forum/topic/official-hardtops-thread
https://pinside.com/pinball/forum/topic/installing-barakandls-nvram-battery-eliminator-vids-review
https://pinside.com/pinball/forum/topic/freeplay40-ramps
https://pinside.com/pinball/forum/topic/important-announcement-from-starship-fantasy -- (reproduction ramps)
https://pinside.com/pinball/forum/topic/new-mantis-parts-available
Feel free to post any other helpful restoration guides (I will try to keep updating the main list). I kept jumping between topics and thought it would be nice to have all the biggies in one place.