Instruction videos are great especially for the complete beginner. I have been to 3 clinics I think (Avery and Will, and guys from our local club that crush) and watched countless videos back in the day. However, problem with instruction videos are that especially beyond the beginner stuff, the smaller hitches one may have in their mechanics may vary wildly, and the broad guidelines from the beginner videos (which unsurprisingly are pretty much the same across different videos) that usually fix 90% of the major problems in peoples throwing motions are not addressing the specific problems.
Another problem of video instruction is that there is no way (other than video) of knowing whether you are doing it right and getting the benefits (or even worse, not doing it but even picking up new bad habits).
For example, I know what I should do to get well past 300ft, and at times I may even think I do it like I should, but then on video I can see I am nowhere near the body positions I should be in. Thousands of incorrect repetitions are locked in too well for me to escape them on my own, at least not too easily.
Therefore, IMO, the only good option is personal coaching, prefereably live, by a professional. They will be able to see what is going on, and with any expertise, why said thing is going on, and suggest ways to get away from that bad habit.