This trading strategy used to be defined as spread trading where you would take profits where small gaps expanded and contracted between the bid and the ask price for a stock. This strategy has now evolved to include technical indicators, support/resistance levels, and volume spikes to make round-trip trades lasting seconds to a few minutes. The basic idea of scalping is to take advantage of market inefficiencies using speed and high trading volume to create quick profits. Click here for more information on scalping.
Assess how much capital you're willing to risk on each trade. Many successful day traders risk less than 1% to 2% of their account per trade. If you have a $40,000 trading account and are willing to risk 0.5% of your capital on each trade, your maximum loss per trade is $200 (0.005 x $40,000). Set aside a surplus amount of funds you can trade with and you're prepared to lose. Remember, it may or may not happen.