It's hard to like bear markets and the portfolio drops that often come with them. But bear markets don't have to be all bad; they can be a time for opportunity -- especially for investors with time on their side. As the stock market continues in its downturn, who better to lean on for investing advice than legendary investor Warren Buffett?

Through his company, Berkshire Hathaway (BRK.B 0.35%), Buffett has put together an investing resume as impressive as they come. What's even better is that his are strategies anyone can adapt and use. Here are a few you can use to lead you through this bear market.

Now's the time to go discount shopping

There are various investing styles. Some people prefer income-producing stocks, some prefer growth stocks, some prefer to look for value, and some prefer a mixture.

Buffett is known as one of the biggest proponents of value investing, which involves investing in stocks trading below their intrinsic value and looking to profit once the market eventually prices it correctly. For instance, if a stock is trading at $100, but an investor believes the intrinsic value is $120, they'd invest, looking to eventually profit from the 20% increase.

Buffett once sent out a letter to his partners saying, "This is the cornerstone of our investment philosophy: Never count on making a good sale. Have the purchase price be so attractive that even a mediocre sale gives good results." In other words, if you're investing in undervalued businesses, you don't have to rely on outsized gains to make good money; you just need the market to come to its senses.

With stocks dropping across the board, now is a good time to grab some great companies trading at discounts or levels not seen since the early 2020 bear market. And Buffett's Berkshire Hathaway has done just that, buying more than $4.1 billion of Taiwan Semiconductor Manufacturing (TSM 2.16%) shares (which are down over 42% year to date) in its third quarter, for example.

Use dollar-cost averaging

Dollar-cost averaging is an investing strategy in which you invest set dollar amounts on a set schedule regardless of stock prices at the time. It's easier to invest consistently when stock prices are rising, but not so much when you're investing during down periods and seemingly "losing" money right before your eyes. Dollar-cost averaging aims to keep investors consistent.

Buffett is an advocate of dollar-cost averaging for most investors. Regarding time spent researching investments, he once said, "If you like spending six to eight hours per week working on investments, do it. If you don't, then dollar-cost average into index funds."

Another benefit of dollar-cost averaging is that it helps avoid situations where investors try to time the stock market. If stock prices are consistently dropping during bear markets, it can be tempting to pause your investing until a later time because you think you can get the same stocks for cheaper then. You may be right. You may also be wrong. Timing the market is all but impossible to do with consistent accuracy over the long run, and you don't want to get in the habit of trying it.

Take Buffett's advice and use dollar-cost averaging -- not only during bear markets, but in general.

Lean on the S&P 500

The second part of Buffett's recommendation of using dollar-cost averaging is investing in index funds. However, he doesn't hold index funds equal -- he believes the S&P 500 (^GSPC 1.08%) reigns supreme. Buffett has long preached that you don't need a portfolio of hundreds of individual stocks or expensive mutual funds; you only need an S&P 500 index fund.

Regarding investing for retirement, Buffett told CNBC that investors should "consistently buy an S&P 500 low-cost index fund" and that he thinks "it's the right thing that makes the most sense practically all of the time." And bear markets may be the perfect time to increase (or begin) your S&P 500 stake. "Keep buying it through thick and thin, and especially through thin," Buffett added.

The S&P 500 is a great option because it's well diversified, contains blue chip companies, pays dividends, and the respective funds are generally very low-cost. It's a good go-to if you essentially want your portfolio to grow with the U.S. economy. Also, the historical results are there: It's averaged around 10% annual returns over the long term. Of course, we can't predict that it'll continue, but there's also no reason to believe the S&P 500 won't continue to be a great long-term option for investors.