Sometimes investors need to be reminded just how unpredictable equity markets can be. Any big, unforeseen event—such as the United Kingdom's so-called "Brexit" vote to leave the European Union—can result in dramatic market swings. And because such fluctuations are as inevitable as they are unpredictable, it makes sense to be prepared for all possibilities.

The best way for most investors to deal with short-term volatility is to stick to a long-term plan, rather than panicking or making ill-considered market moves. And your plan will need a proper balance between stocks and bonds in your portfolio. Historically, stocks have outperformed other kinds of investments and have provided a hedge against inflation, while bonds have provided steady income and more protection against market volatility.

Diversification and asset allocation—core principles for attempting to control investment risks—are used to create a portfolio that may have the breadth to reduce volatility when markets get turbulent. Your overall tolerance for risk can help determine how you allocate your investments to stocks, bonds, and other assets. Diversification and asset allocation are designed to minimize inherent risks, although there are no absolute guarantees.

But as important as it is to choose a mix of investments that makes sense for you, you'll also need to revisit your portfolio periodically to help restore the balance you've established. If stock prices rise, for example, that part of your portfolio may grow larger than you intended—and this could make you vulnerable if equity prices fall. "Rebalancing" helps you get back to the target percentages you started with.

Yet as simple as that may sound, rebalancing can seem counterintuitive in practice. It requires you to sell investments that have been doing well and buy others that have slumped. Your natural inclination may be to keep riding a wave of success, and to stay away from parts of the market that haven't performed well.

But rebalancing can help impose needed discipline for your plan. It can enable you to sell high and buy low and to maintain the broad balance that may cushion your holdings against volatility. And though it sometimes may result in a lower rate of return than you would have gotten if you'd let your winning positions continue to grow, that may be a small price to pay for feeling more comfortable about your investments.

Rebalancing also can help you resist the impulse to try to "time" the market—attempting to jump in when prices are rising and to get out before they fall. That is rarely a recipe for success and could lead to significant losses.

How often should you rebalance? Expert opinions vary, but you probably should review your portfolio and rebalance at least once a year. The end of the year could be a good time to get your ducks in a row.