Practice, practice, practice. But not with real money. There’s nothing better than hands-on, low-pressure experience, which investors can get via the virtual trading tools offered by many online stock brokers. Paper trading lets customers test their trading acumen and build up a track record before putting real dollars on the line. (Several of the brokers we review offer virtual trading, including TD Ameritrade and Interactive Brokers.)
A few decades ago, most buyers and sellers were individual investors, such as wealthy businessmen, usually with long family histories to particular corporations. Over time, markets have become more "institutionalized"; buyers and sellers are largely institutions (e.g., pension funds, insurance companies, mutual funds, index funds, exchange-traded funds, hedge funds, investor groups, banks and various other financial institutions).
People trading stock will prefer to trade on the most popular exchange since this gives the largest number of potential counter parties (buyers for a seller, sellers for a buyer) and probably the best price. However, there have always been alternatives such as brokers trying to bring parties together to trade outside the exchange. Some third markets that were popular are Instinet, and later Island and Archipelago (the latter two have since been acquired by Nasdaq and NYSE, respectively). One advantage is that this avoids the commissions of the exchange. However, it also has problems such as adverse selection. Financial regulators are probing dark pools.