Set a process for identifying future cash flows and based on that try to calculate intrinsic value of a company.
Read what is written by Warren Buffett in his letters to shareholders.
While writing about Calculation of Intrinsic value in the Owners manual Buffet says...
Intrinsic value is an all-important concept that offers the only logical approach to evaluating the relative attractiveness of investments and businesses. Intrinsic value can be defined simply: It is the discounted value of the cash that can be taken out of a business during its remaining life.
The calculation of intrinsic value, though, is not so simple. As our definition suggests, intrinsic value is an estimate rather than a precise figure, and it is additionally an estimate that must be changed if interest rates move or forecasts of future cash flows are revised. Two people looking at the same set of facts, moreover — and this would apply even to Charlie and me — will almost inevitably come up with at least slightly different intrinsic value figures. That is one reason we never give you our estimates of intrinsic value. What our annual reports do supply, though, are the facts that we ourselves use to calculate this value.
Read owners manual on http://www.berkshirehathaway.com/