I am trying to work on my quantitative method. I took basic OLS regession, and now I am reading basic econometrics which cover experiments, regression, instrumental variables, and differences-in-differences. In what topics should I go beyond these? I am thinking of looking into time-series analysis. Really appreciate if any quantitative folk can give me a list of essential quantitative topics I should cover. Also, my statistical skills are limited to basic probability, variability. Do you guys think taking casual inferences from pure statistical field would be helpful to advance on my quant method?