The past month has probably been stressful for many investors. The S&P 500 index, arguably the most common placeholder for the U.S. stock market, has declined over 8%, flirting with a technical correction (10% decline from peak). What's been hard for many is the speed at which things have moved; numerous down days can be jarring, especially after the market has been so strong since early 2023.

First, and most importantly, take a breath. Stock market corrections are perfectly normal and a symptom of a healthy investing climate. Could the market continue falling? Of course! However, market volatility is a feature, not a weakness. Look at any long-term price chart: The S&P 500 index is arguably the most dependable long-term wealth generator available to the individual investor.

If you want to make money in stocks over the long haul, you will want to buy when prices fall. You would happily buy a big-screen TV when it goes on sale. Why should stocks be any different?

However, there are optimal ways to do things. Here is the smartest way to invest in the S&P 500 in March 2025.

Find a high-quality S&P 500 index fund

Did you know that you can't directly invest in the S&P 500? Fortunately, certain mutual funds, called index funds, exist that you can buy. Index funds replicate a specified stock market index, including the companies and their weights. For those who want to invest in the S&P 500, the Vanguard S&P 500 ETF (VOO 2.05%) is an excellent way to go.

There are other choices, but Vanguard is among the most trusted names in the investing community. Plus, I like that the Vanguard S&P 500 ETF has a low expense ratio of just 0.03%. In other words, you'll only pay about three pennies to Vanguard for every $1,000 you invest. Low fees are essential so that most investment returns go to you, not the fund's management.

You can see below how the Vanguard S&P 500 ETF has closely followed the actual index over time:

VOO Total Return Price data by YCharts

Buy slowly, and continue adding savings

Now that you know where to invest your money, it's time to consider how to deploy your hard-earned capital.

One of the most common investing mistakes is trying to time the market by going "all in" at once. Nobody knows what the stock market will do in the short term. It could continue falling or soar to new highs by the end of March. It's anyone's guess, and while it can be lucrative to guess correctly, investors can lose a lot if they go all-in just before a severe downturn. At that point, you're essentially gambling.

The smarter approach is to buy a little at a time, regardless of whether prices are up or down. This is called dollar-cost averaging. The goal is to wade into the market slowly. If prices go up, you'll be glad you started buying. If they fall, you'll be happy you didn't jump in with both feet.

Think in terms of years, not months

At this point, let's assume you've identified an S&P 500 index fund and created a plan to deploy funds slowly. The last step -- the most important -- is having the proper mindset.

Remember that while the stock market may look like letters and numbers on your brokerage account, it represents real businesses with assets and profits. Investing alongside the S&P 500 means owning little pieces of hundreds of America's leading companies. It's like you're partnering with them as a minority owner.

^SPX data by YCharts

Prices will fluctuate based on the market's emotions but eventually follow earnings. If America's best companies continue growing earnings, the S&P 500 will take care of investors over the long haul. Think in terms of years, not months, and don't let the volatility distract you from that simple truth.