Y Combinator Sales Summer School: https://www.youtube.com/watch?v=t-K2DHi99oI&list=PLb1c0oEEXW...
This is basically Sales 101. Lecture by Steli Efti, YC founder of the close.io CRM. Insanely valuable.
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Y Combinator "How To Start A Startup" Sales: https://www.youtube.com/watch?v=SHAh6WKBgiE
This is held by one of the founder of YC startup Clever, with an emphasis on the earliest stages of sales in a startup.
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Tons of specific sales advice on http://blog.close.io , you can find the best by googling "site:blog.close.io" and follow through the links. There is a ton of things I learned from Steli Efti (the guy behind www.close.io CRM and the Sales Summer School), be sure to attend their webinars as well if you're curious.