The reason is because all too often the price can drop and you will end up giving up that profit. Instead, as soon as I’ve reached my first profit target (if I’m risking $100, then as soon as I’m up $100), I’ll sell 1/2 my position and set my stop at breakeven. This method of scaling out ensures small profits on all trades that move in your favor, giving you a better percentage of success.
In addition to knowledge of basic trading procedures, day traders need to keep up on the latest stock market news and events that affect stocks—the Fed's interest rate plans, the economic outlook, etc. So do your homework. Make a wish list of stocks you'd like to trade and keep yourself informed about the selected companies and general markets. Scan business news and visit reliable financial websites.