What is the best things you depended on it when you want to invest in any company or buy it

you need to go through the previous financials and their movements. A through financial analysis are a must before talking any decision. other than financial analysis brand name is also important as it shows the goodwill of the company and can give you a better understanding.  

Financial statements as a whole will provide the maximum benefit in the company's evaluation process. I believe value investing is the most proven method for the long term. Also, breaking down DuPont equation and assessing each profit margin, asset turnover, and debt ratios is crucial in being a successful investor. 

I would say that cash flows analysis provides greater insights on company's performance, going forward.  However, income statement and balance sheet analysis also supplement the arriving at the right conclusion.  A healthy company has a consistently strong operating cash flows that are used to derive profitable growth and pay dividends.