It's been a fantastic summer as an intern here at The Motley Fool. In many ways, I feel as if I was paid to learn, and this is one of the best environments to do just that. I have barely scratched the surface of an investing education, but as with many things in life, learning the fundamentals first leads to the greatest rewards. Here are the 10 best things I learned about investing this summer:

1. First thing to look for: a firm's market opportunity. It seems obvious, but if you're looking for growth, you'd better make sure there's room to grow.

2. As an investor, never bet against convenience. Netflix is a great company, but the Qwikster fiasco failed because it altered the company's value proposition: aggregating content in one location. For consumers, one click is always better than two.

3. There's no substitute for active reading and learning (pen in hand, and choosing primary sources over secondary). Charlie Munger once said Warren Buffett accomplished his outstanding investment performance by "sitting on his ass and reading."

4. Be a skeptic when reading. Behind every shareholder letter and analyst report, there is an incentive. Awareness of those incentives can help you avoid mistakes.

5. Build an investing checklist and do everything possible to eliminate cognitive biases. Here's an example of a qualitative checklist I built for myself:

  • Do I understand the business model -- i.e., how does the company make money?
  • Is it a company I enjoy following to the extent that I will continue to follow it for the next five to 10 years?
  • Does the company have a sustainable competitive advantage?
  • Does the company have a significant market opportunity?
  • Does the company have the ability to raise prices? Ask yourself if you would pay more for the product or service (even a sample size of one can be illuminating in this regard).
  • Do I trust the company's leadership -- i.e., are they honest, do I admire them, what's their character?
  • Does the company have competitors, and if so, why shouldn't I buy them? Looking broader, are there better companies I could buy for the same market cap?
  • Is the company in a growing or sustainable industry?
  • What are the potential industry disruptors?
  • Will they be doing or selling more of what they do or sell in five years?
  • Is this a balance sheet or an income statement company? Is this a manufacturing or a distribution company? (These two questions tell you where to focus and they can be trickier than they seem.  For example, fellow Fool Buck Hartzell often points out that Coca-Cola's advertising claims they make the best soft drinks, but their true strength lies in distribution.)
  • Have you discussed this with at least three people who disagree with you?

6. If you have a great experience with a company, buy some shares. Skin in the game keeps you interested.

7. When the market goes up, it's OK to check your stocks frequently. When the market goes down, as long as your investment thesis remains intact, spend less time checking and more time doing the things you enjoy. You're winning either way.

8. Time is the advantage the individual investor has over the institutional investor. Furthermore, the longer your holding period, the less it matters whether the stock is selling at a premium or a discount.

9. A stock's fair value is impossible to predict to an exact degree, but you should still use accepted techniques to come up with estimates to aid your decision within the broader context of your qualitative investment frameworks. Warren Buffett points out that if you have to go to the fifth decimal in your valuation to make money, you're looking at the wrong company.  

10. There is no catch-all strategy when it comes to investing. If you're not willing to actively learn, then indexing is the way to go.

These 10 points are just the first of many that I hope to learn over the years. Here is my pledge: Every year I will publish the 10 best things I have learned about investing during that year. For the greatest investors, learning never stops. I am a long way from being a great investor, but I'll see you next year nonetheless.