The economic strength of these two economies dictates the performance of this major forex pair and as such, important indicators are the GDP and the performance of the labour market (i.e. unemployment rates and wage growth metrics).
As is the case with all national currencies, the monetary policies and interest rate decisions of the Federal Reserve Bank in the U.S and the Bank of Japan will likely influence investor sentiment in this pair.
Also, since the Japanese economy is heavily reliant on commodities, traders can look to international import and export figures to determine the future market direction.