The "How to Start a Startup" Series by Y Combinator

Getting accepted into their program is harder than getting into an Ivy League school. However, they have a TON of free resources on their website, including lectures, essays and videos by their own (very famous) staff and famous founders of big companies that you would recognize. Most companies don't need to aim for billions of users; however their advice is really applicable to companies of any size.

One of the previous Presidents of Y-Combinator is Sam Altman, who is now very well known as the head of the artificial intelligence company OpenAI.  He has several articles available that are great resources for all kinds of founders.

If you are in the early stages, there is a two part lecture that is especially great for you! Sam delivers insights into "ideas, products, teams and execution," while his famous co-lecturer Dustin Moskovitz discusses the "why" to start your own business. 

Lecture series click HERE 

Pro-tip: you can read the transcript if you want to get through the info speedier! That transcript link is HERE but you can find it on the video page too.