Strongly recommended
Basic Soldering Lessons 1 - 9
Why people recommend it
The old PACE soldering training films, still considered the best grounding in proper technique despite their age and dated production.
Watch for: Start with the first lesson; the first three cover the essentials
In their words
I must take this chance to advertise my absolute favourite soldering video: Basic Soldering Lessons 1-9, made in 1980 by PACE.
pipe on electronics.stackexchange.com, Oct 2016. CC BY-SA.