Game development is a difficult field to break into. Many people have recognized this and, in an effort to make the profession more open and available to anyone who wants to work in it, have created plenty of video guides to getting started or continuing learning game development.
Straight from the Game Developers Conference, GDC Vault is a service provided by Gamasutra that catalogues and retains all of the presentations given at GDC in past years. Topics covered include everything from programming, to art, to music and more. GDC Vault holds some of the most professional and well-done videos related to game development.
Extra Credits is a video series that publishes new videos once a week. Supported through crowdfunding, all of their videos are completely free and cover a variety of game design topics. Alongside their main series, Extra Credits also runs a podcast, publishes articles, and maintains an active forum.