Everyone will have their own opinion on this subject. For me the best technical painting book I’ve ever read and always re-read, is “Alla Prima ii” by Richard Schmid, I’d reccomend it to all artists whatever their stage.

Alla Prima is not a technique I use but the amount and standard of advice within the book is astounding, and crosses over all types of painting. The narative is very down to earth and encouraging. It’s quite expensive but worth every penny.