For most people, the best choice for long-term investing is to do nothing else but to keep buying an exchange-traded fund (ETF) which tracks the S&P 500. This increasingly popular approach is called passive investing. Examples of ETFs which track the S&P 500 are the S&P 500 ETF (symbol SPY), Vanguard S&P 500 (symbol VOO) and the iShares S&P 500 (symbol IVV). Each is an excellent approximation of the U.S. economy, the strongest economy in history.
Given how little time and effort is needed, the results will be remarkably good if allowed to compound over many years. Albert Einstein stated that compound growth is the eighth wonder of the world.
Even Warren Buffett, widely considered among the best investors in history, has failed to beat this record over the last five years. In fact, he wants 90% of his estate to be placed in an exchange-traded fund (ETF) which tracks the S&P 500.
In his 2017 annual report to shareholders he states:
I believe the long-term results from this policy will be superior to those attained by most investors — whether pension funds, institutions, or individuals — who employ high-fee managers.
Here is the track record of this approach to investing.