There are two main strategies that are used to pick stocks on the market, fundamental investing and technical analysis.
Fundamental Investing aims to find the true intrinsic value of the business/stock and buy it at a discount to what is is trading now. It looks at underlying factors that influence the stock and the future prospects of the company. In theory, if you have bought a good company trading below its intrinsic value, you will do well over time.
This means that a fundamental investing is usually a long term strategy for trading stocks. They do not try to time the market or buy and sell on certain swings, but hold until the company intrinsic value of the company changes, by then, hopefully making a large capital gain.
To find out more about fundamental investing and for a more detailed look at the terms surrounding it, have a look at the investopedia entry on the strategy: Fundamental Investing
I also like Rodger Montgomery's value investing strategy for picking well performing stocks, his blog and insights can be found here
Technical Analysis or "chartists" aim to find structural and technical patterns based on previous performance of the stock in an attempt to ascertain future price movements. T/A's try to time the market conditions when buying and selling a stock and use various technology and analysis such as candlestick charting and volume/price analysis to make their decisions. Again for a more in depth study on technical analysis see the invesopedia entry on T/A
