Anything related to the central bank will have a large impact, as they are the ones who determine interest rates, and interest rates have a big effect on currency flows.
GDP is also important, as when there is an economic slowdown it may result in the central bank reducing rates to boost economic activity. The opposite is also true, large increases in GDP may mean that an interest rate hike might be needed.
Inflation data is also very important. Again, large changes in inflation either way may push the central bank towards changing rates. This data typically is in the form of CPI
Note that each central bank is different. They all have specific mandates and specific pieces of economic data that they place emphasis on. The Federal Reserve as of late has closely been watching inflation data, especially wage inflation data, and employment. Significant deviations in these data points from whats expected by investors can greatly move the market. However, these specific factors are a little less important for, say, Mexico, which is mostly concerned with headline inflation. Read the statements issued by the central banks to find out whats important to them.
Central banks also issue expectations for things like growth, CPI, etc. If these expectations are not met, it may result in a policy change, or at least talk of a policy change, at the next meeting of the central bank. Anticipating these policy changes and trading accordingly is one strategy to be a profitable forex trader
Also, there are several forex news calendars online that indicate what is likely to be high impact news. These can be helpful starting out.