Risk management - Rather than looking for one big trade, the way a trend trader might, the scalper looks for hundreds of small profits throughout the day. In this process the scalper might also take hundreds of small losses during the same time period. For this reason a scalper must have very strict risk management never allowing a loss to accumulate.
Define and write down the conditions under which you'll enter a position. "Buy during uptrend" isn't specific enough. Something like this is much more specific and also testable: "Buy when price breaks above the upper trendline of a triangle pattern, where the triangle was preceded by an uptrend (at least one higher swing high and higher swing low before the triangle formed) on the two-minute chart in the first two hours of the trading day."
The bid–ask spread is two sides of the same coin. The spread can be viewed as trading bonuses or costs according to different parties and different strategies. On one hand, traders who do NOT wish to queue their order, instead paying the market price, pay the spreads (costs). On the other hand, traders who wish to queue and wait for execution receive the spreads (bonuses). Some day trading strategies attempt to capture the spread as additional, or even the only, profits for successful trades.
Scalping can be very profitable for traders who decide to use it as a primary strategy, or even those who use it to supplement other types of trading. Adhering to the strict exit strategy is the key to making small profits compound into large gains. The brief amount of market exposure and the frequency of small moves are key attributes that are the reasons why this strategy is popular among many types of traders.
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.