From your qyestion i presume that you are thinking about investing in an Exchange Traded Fund (ETF) that mirrors ab index like the S&P BSE Sensex or Nifty 50 and so on.
In order to invest in such instruments you do not need to make any special efforts like reading books. You do not even have to compare the relative performance of various funds that offer same product, simply for the reason that ultimately the returns depend on the performance of the fund dependson the performance of the underlying index and not the fund manager. That is the reason such funds are called passive funds.
What is 'Crucial' though is that after you have made a single investment or a series of regular investments (latter is preferable ), you simply leave the investment undisturbed for 20 to 50 years, providing an opportunity for