Taking tips from successful investors is a great way to get ahead in the stock market, and Warren Buffett is an exceptional role model. His shrewd insight, coupled with his pragmatic approach to business, has made Berkshire Hathaway, the company he leads, one of the largest public companies in the world.

That success has made Buffett one of the wealthiest investors in the world, too. According to Bloomberg, his fortune is currently valued at $110 billion. With that in mind, here are three pieces of advice from Buffett that are particularly relevant now.

A bear market is a buying opportunity

The Great Recession devastated many investors. The housing market collapsed, the S&P 500 lost 56% of its value, and several high-profile financial firms filed for bankruptcy. Buffett saw the downturn as a buying opportunity, and in 2008, he wrote these words in an op-ed piece for the New York Times: "A simple rule dictates my buying: Be fearful when others are greedy, and be greedy when others are fearful."

Investors tend to be overly optimistic during good times and overly pessimistic during bad times. It happened during the Great Recession, and it's happening again today. Patient investors can capitalize on that quirk of human nature by treating fear-driven downturns as buying opportunities.

Invest in companies with a competitive advantage

In his 1995 letter to shareholders, Buffett said, "In business, I look for economic castles protected by unbreachable moats."

A moat is a competitive advantage -- a quality or asset that protects a business from its rivals. Moats come in different shapes and sizes, and terminology may vary from one source to the next, but four of the most common moats are network effects, intangible assets, cost advantages, and high switching costs.

Network effects occur when each user increases the value of a product or service for all existing users. Amazon (AMZN -0.29%) is a textbook example. Each seller brings more inventory to the marketplace, creating value for every buyer, and each new buyer brings more purchasing power to the marketplace, creating value for every seller.

Of course, the potency of a network effect depends on the size of the user base. Amazon, however, operates the most visited online marketplace in the world, so it benefits from a particularly powerful network effect.

Intangible assets refer to patented technology, brand authority, or other non-physical attributes that give a company an edge. Cybersecurity-specialist CrowdStrike is an excellent example.

Its platform crowdsources data on an unmatched scale, making its artificial-intelligence engine uniquely effective in detecting threats. That quality has made the CrowdStrike brand synonymous with industry-leading protection.

High switching costs make it hard to change vendors. Shopify (SHOP -0.64%) is a good example. Its platform allows merchants to manage their businesses across physical and digital channels, and the company offers adjacent services like payment processing, financing, and fulfillment.

After building a business on the Shopify platform, it would be very troublesome for a merchant to switch vendors. That advantage, coupled with the company's broad product offering, has made Shopify the market leader in e-commerce software.

Cost advantages allow a business to produce a product or provide a service at a lower cost than the competition. Tesla is a fantastic example.

Proprietary battery-cell technology allows the company to produce battery packs -- the most expensive part of an electric car -- at a lower cost per kilowatt-hour than any other automaker. That advantage helped Tesla achieve an industry-leading operating margin in the most recent quarter.

Think long term when buying stocks

In his 1996 letter to shareholders, Buffett told investors, "If you aren't willing to own a stock for 10 years, don't even think about owning it for 10 minutes."

That doesn't mean you must hold every stock for a decade. As my colleague Keith Speights points out, Buffett has broken this rule from time to time. But a long-term mindset is still critical. It gives your investment thesis time to play out and corrects for short-term market volatility.

In a nutshell, investors should ask themselves a few questions before buying a stock. How much could the company be worth a decade down the road? Is the company successfully executing on its market opportunity?

Another question to include: Is the current share price reasonable, compared to the long-term potential? If you're satisfied with the answer to those questions, the stock is probably worth buying.