Pruning is complicated, not only do the different species require a different approach, but same varieties, particularly with apples, have their own traits that require different management. Apples are the most complicated, at least when dealing with semi-standards from M7 up. Once apples are bearing you can learn faster by waiting to prune until flower buds are clearly visible at first growth in spring. At that time you can clearly see where the flower buds of a variety form which will help you decide what you can afford to remove.
Scott didn’t include it in the general reference pages above, but I know that some people find the article I wrote about pruning by numbers (ratios) very helpful- Lee Calhoun wrote me a personal thank you note when he received it and told me it cleared up confusion that had plagued him for 20 years. Yes, that is a boast, but I’ve spent so much of my life trying to figure out pruning that I would like to think the knowledge I’ve acquired is generally useful. What is unique about my explanation is that it includes actual numbers and distances needed to achieve adequate spacing of branches, such as distance between tiers in a central leader tree and how far branches should be allowed to spread in upper tiers.
Of course, videos provide visual information more difficult to extract from words, but words are necessary to explain concepts. When I was learning to prune I used both and gradually learned the reasons for contradicting instructions.
That said, even though I do more fruit tree pruning in a season (maybe in a month) than a home orchardist is likely to do in a lifetime, decisions can still be challenging. If that wasn’t so, I doubt I’d still find pruning all day long, 6-7 months of the year still interesting.
Incidentally, the idea of pruning back scaffolds on young apple trees by a third is the traditional method, but it is generally not employed by anyone involved with commercial production unless a specific variety demands it to achieve adequate rigidity in the branches to support a crop. It can also be used to encourage secondary branching, but commercial growers tend to use temporary scaffolds with varieties like Honey Crisp that are not cooperative at branching out. I use the temporary branches to tape uprights from permanents to horizontal which takes care of secondary branching problems pretty quickly.