The goal of most investors generally is to buy low and sell high. This can result in two quite different approaches to equity investing.
One approach is described as "trading." Trading involves following the short-term price fluctuations of different stocks closely and then trying to buy low and sell high. Traders usually decide ahead of time the percentage increase they're looking for before you sell (or decrease before they buy).
While trading has tremendous potential for immediate rewards, it also involves a fair share of risk because a stock may not recover from a downswing within the time frame you'd like—and may in fact drop further in price. In addition, frequent trading can be expensive, since every time you buy and sell, you may pay broker's fees for the transaction. Also, if you sell a stock that you haven't held for a year or more, any profits you make are taxed at the same rate as your regular income, not at your lower tax rate for long-term capital gains.