Mark Rosewater gave a great talk this year regarding design lessons he’s learned as a designer (currently lead designer) on Magic over 20 years.  This talk is so good that it should be used on day one of most Design 101 courses.

Incidentally, much of this talk comes from the best lessons from his column, “Making Magic”.  This blog is probably the best long-running game design blog in the industry, and if you like and understand Magic, you should be reading it.