Investors with a long horizon and not a great deal of time for research might consider regular purchases of mutual fund shares. Mutual funds invest in a number of different assets, so one need worry less about diversification than if buying individual common stocks. Moreover, they are frequently available at relatively low cost for the management of one's invested money.
By dollar cost averaging (investing essentially the same dollar amount at regular intervals, such as monthly, quarterly, or annually), one tends to buy more shares when the market and one's preferred mutual funds are lower in price, fewer when they are higher, thus reducing the overall cost basis. Especially if investing in tax-deferred accounts, such as Roth or regular IRAs or in 401K Plan accounts, one may simply direct that capital gain and dividend distributions be reinvested upon receipt in the account and leave one's holdings alone for decades at a time, allowing one's investments a chance to develop good compound total returns.
It is useful to analyze a group of mutual funds periodically to see if they still warrant inclusion in one's portfolio, but caution is appropriate before selling out and switching to a new fund. Often, one gets fearful or impatient and sells lower performing mutual funds at just about the wrong time, then investing the redeemed dollars in other funds that have performed quite well, just before they return to more modest levels of performance, losing out in both steps.