The months of campaigning are over, votes have been tallied, and the result is known: the UK has voted to leave the European Union.

Clearly, this is a significant issue for most investors. At time of writing the FTSE 100 is down by around 5% implying that very few investors will come out of this unscathed. And now uncertainty prevails, in the short term at least it’s likely that markets will only go down as traders and investors around the world position themselves for the worst.

For most Foolish investors, the best course of action to take after today’s result is to do nothing at all. Financial markets have a habit of over-reacting, they have done since the beginning of time, and it’s unlikely to be any different this time around. A knee-jerk reaction to sell isn’t usually the best course of action and is likely to do your portfolio more harm than good.

What does the result mean for you? 

What today’s results means for your portfolio will probably depend on your individual circumstances. If you’re a short-term trader, then the market volatility will have more impact on your portfolio than a long-term investor.

However, Foolish long-term investors should look past today’s volatility and market shock and concentrate on what happens over the next few weeks and months. If the UK can quickly work out a deal with the rest of Europe, then market stability should return relatively soon. 

If the divorce takes longer to thrash out than expected, then it could take some time before normality returns but over the long-term, it’s likely markets will recover, and the UK’s economy pushes forward.

Time to take action

So, how should Foolish investors approach the market today? Most Foolish investors should turn off their screens and walk away to prevent any emotion-driven trading. Then it could be time to hunt for bargains as opportunities present themselves. Defensive stocks that have been sold off are probably the best bets with income champions like Imperial Brands, British American Tobacco, GlaxoSmithKline, AstraZeneca, Royal Dutch Shell Plc and Reckitt Benckiser Group Plc all trading down in early deals. These companies are unlikely to be severely impacted by a Brexit and any declines present an excellent opportunity for long-term investors to buy. Gold miners such as Centamin and Randgold Resources may also be attractive plays on the price of gold.

On the other hand, it may be best to avoid financial companies as the outlook for firms in this sector has suddenly become very uncertain. The City of London thrived on the ‘passporting’ rights afforded to it by the EU, giving the UK’s banks access to 500m customers and a European economy nearly 10 times the size of the UK’s. Without access to the single market, life might suddenly become difficult for the City of London. This is reflected in the decline of bank stocks some of which have fallen 30% in early deals. 

If you want to make the most of today’s trading action and snap up some bargains, the best option maybe to by a low-cost FTSE 100 tracker fund. At the time of writing the index supports an average yield of 4.3% and is broadly diversified with 100 stocks all contributing to this payout.  

 The worst mistake you could make

According to a study conducted by financial research firm DALBAR, the average investor realised an average annual return of only 3.7% a year over past three decades, underperforming the wider market by around 5.3% annually.

This underperformance can be traced back to several key mistakes that all investors make. To help you realise and understand the most common mis-steps, the Motley Fool has put together this new free report entitled The Worst Mistakes Investors Make.

The report is a collection of Foolish wisdom, which should help you avoid needlessly losing too many more profits. Click here to download your copy today.

Rupert Hargreaves has no position in any shares mentioned. The Motley Fool UK has no position in any of the shares mentioned. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors.