Quote from jonp:
real scalping is holding a position for 2 minutes or less on average. you are using a stock which is low priced, has a 1 cent spread between bid/ask. you have the level 2 quotes of the stock your watching as well as the time and sales right in front of you flashing every sale price and quantity. you put an order for 100 shares on the bid, 100 on the ask. you wait for your fills and you make $1 each way.
I started working for a prop firm doing this in April. at that point it was still effective. and then everybody started using midpoints, which cut the profits in half. it wouldn't have been that bad though if volume didn't die out too. now the levels break, or switch sides very quickly due to the low volume fast moving market. After 3 months working at my place i quit because it was just ridiculous, trading with no strategy, with no overnight holding power. anyway i've been day/swing trading stocks/etfs/forex, and I am much much more profitable this way.
If you're at a place like mine, it doesn't hurt to just stay for a few months getting experience seeing price action all day long. it will help you with your entries and exits later on.