You could start out by thinking of some assets or stocks that are trading at extremely high or low levels compared with what you believe they are worth. This may produce some ideas which may help you decide on which metrics (P/E, book value, sentiment and so on) you will use to determine whether the company is overvalued or undervalued. Then decide at what levels these metrics warrant a trade and how and when you will enter and exit when these levels present themselves. This is how to start building a contrarian investing strategy.