Take profits near the upper channel line. If the market is strong, you can wait for the channel line to be hit. If it's weak, grab your first profit while it's still there. What if a strong swing overshoots the channel line? An experienced trader may shift his tactics and hold a little longer, perhaps until the day when the market fails to make a new high. A beginning trader is better advised to take profits after the channel line has been hit as it's important to learn to take profits in accordance with one's trading plan.
The price movements of any stock are posted throughout the trading day and summarized at the end of the trading day. For example, April 2, 2019, shares of Apple Inc. (AAPL) opened at $191.09 and closed at $194.02. During the day, as indicated in the "day's range" listed to the right of the closing price, shares dropped as low as $191.05—the intraday low—and hit a peak of $194.46—the intraday high.
Smaller moves, easier to obtain - A change in price results from imbalance of buying and selling powers. Most of the time within a day, prices stay stable, moving within a small range. This means neither buying nor selling power control the situation. There are only a few times which price moves towards one direction, i.e. either buying or selling power controls the situation. It requires bigger imbalances for bigger price changes. It is what scalpers look for - capturing smaller moves which happen most of the time, as opposed to larger ones.

Many swing traders assess trades on a risk/reward basis. By analyzing the chart of an asset they determine where they will enter, where they will place a stop loss, and then anticipate where they can get out with a profit. If they are risking $1 per share on a setup that could reasonably produce a $3 gain, that is a favorable risk/reward. On the other hand, risking $1 to make $1 or only make $0.75 isn't as favorable.
Some of the common mistakes that scalpers make are poor execution, poor strategy, not taking stop-losses, over-leveraging, late entries, late exits and overtrading. Scalping generates heavy commissions due to the high number of transactions. A per-share commission pricing structure is beneficial to scalpers, especially for those who tend to scale smaller pieces in and out of positions.
This combination of factors has made day trading in stocks and stock derivatives (such as ETFs) possible. The low commission rates allow an individual or small firm to make a large number of trades during a single day. The liquidity and small spreads provided by ECNs allow an individual to make near-instantaneous trades and to get favorable pricing.
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.