Liquidity - The liquidity of a market affects the performance of scalping. Each product within the market receives different spread, due to popularity differentials. The more liquid the markets and the products are, the tighter the spreads are. Some scalpers like to trade in a more liquid market since they can move in and out of large positions easily without adverse market impact. Other scalpers like to trade in less liquid markets, which typically have significantly larger bid-ask spreads. Whereas a scalper in a highly liquid market (for example, a market maintaining a one-penny spread) may take 10,000 shares to make a 3 cent gain ($300), a scalper in an illiquid market (for example, a market with a 25 cent spread) may take 500 shares for a 60 cent gain ($300). While there is theoretically more profit potential in a liquid market, it is also a "poker game" with many more professional players which can make it more difficult to anticipate future price action.
For most students, once his or her accuracy has improved the next step is increasing positions sizes to maximize profits. If you’ve been trading at 65% success with 1:1 or 2:1 profit loss ratios for at least a couple of months you should be starting to feel pretty confident. Now it’s time to increase your position sizes. Since you’ve been working with a $100 max loss, you’ve probably rarely exceeded 2000 shares.
You're probably looking for deals and low prices, but stay away from penny stocks. These stocks are often illiquid, and chances of hitting a jackpot are often bleak. Many stocks trading under $5 a share become de-listed from major stock exchanges and are only tradable over-the-counter (OTC). Unless you see a real opportunity and have done your research, stay clear of these.