Everyday around the world there are hundreds of reports, interviews and other worthy media events that can affect the markets.
There is one free site that can boil these down in to the most significant events and tell you which of those is the most important.
You need to understand how each report or event will affect the instrument that you are trading. It could cause the market to change direction and you may lose money if you are trading at that time.
One website I like to use is ForexFactory.com
This should be one of your daily rituals: Before you trade check to see what events are happening and when. Then make your trading plans accordingly.