From the Internet:
https://mustcontainminis.com/2021/08/how-to-prep-plastic-miniatures-for-painting.html
https://massivevoodoo.blogspot.com/2020/07/tutorial-how-to-prepare-soft-plastic.html
https://www.polygon.com/tabletop-games/23643118/how-to-paint-miniatures
https://boardgamegeek.com/thread/687047/painting-plastic-minis-how-guide-beginners-warning
https://www.flamesofwar.com/Default.aspx?tabid=110&art_id=5615&kb_cat_id=24
https://themodellingjournal.blogspot.com/p/how-to-paint-your-figures.html
Videos:
https://www.youtube.com/watch?v=a7h9D6uuaso
https://www.youtube.com/watch?v=X_gt4FwG47Y
There is always something to learn!