There are many factors involved in choosing which instruments to trade. Some traders prefer to invest in instruments they know well or can easily obtain information of. Others prefer to trade a variety of instruments, in order to diversify their portfolio, better-manage risks and take advantage of a greater selection of market opportunities. You can choose an instrument by following market analyses or even by simply watching the news. There are a lot of resources offering information about trading opportunities and they could help you decide which instrument to trade.