Being in the market for long I have learned to always know the company before picking stocks for my portfolio. Through the collective knowledge, I have listed down 5 major things that every investor must know about the company for long term investment:

Earning Growth - Check the net gain of the company of a particular period. Check the trend of growth.
Consistency of Stability- Most of the company do affect largely during bad times in the market. Check if the company is struggling while the market has recovered from instability.
Major strength: Is the company's stock help you see a potential future? Check the overall industry and strength.
Debt Equity Ratio- Check the different company's balance sheet, liability, compare the debt-equity ratio. Consider a company with a debt-to-equity ratio of 0.30 or below.
Price Earning ratio: PE ratio is considered to be one of the important factors that an investor must check. It helps to compare and find the required company in the same industry.