For people with spare time and a desire to improve/learn:

General channels featuring the world's top players:

Whatever your hero choice, there are videos on these channels that will give you ideas about all aspects of the game - best place to start.

https://www.youtube.com/channel/UCYx...kHNZirTJxfNLiQ

https://www.youtube.com/channel/UCwW...9JjR1ArMlFljjQ

https://www.youtube.com/channel/UC2a...uOv60-33qJUmYA

Pro comps - ideas for strats/team composition etc:

https://www.youtube.com/channel/UCLE...CTTQIs_JfBKnkw

https://www.youtube.com/channel/UCiM...XGpQ5PaK9kp5VQ

https://www.youtube.com/channel/UC8j...YVgCVVTzWPF75g

Individual player channels:

DPS:
https://www.youtube.com/channel/UC_g...3-Oczaxavv9sxg

https://www.youtube.com/channel/UC29...NDqyaVyShL7VJA (also plays wicked Zarya and Roadhog)

https://www.youtube.com/channel/UCfS...c_b1bwarpI6LGw (Pharah top 500 player)

Tanks:
https://www.youtube.com/channel/UCyk...FLmUMSuryhnS1g

Also search "Miro" on YT

Support:
https://www.youtube.com/channel/UCKe...4DnejVNo5ZSIDQ

https://www.youtube.com/channel/UCAr...qrsLSEDClv3UYw