I invest based on a series of filters which curate the viability or suitability of a stock. So first I'll apply the initial filter which could just be a formula like the valuation formula in this post. Then I'll look at other aspects such as P/E and dividend payout ratio, then I'll look in even more detail, looking at what the company is doing, whether they have secured good deals, who is the CEO and whether or not that CEO is shareholder friendly, does the company have moats, is it selling a niche product or must have product, etc. I get obsessive in my research, once I have a narrow list of stocks to obsess over, and then I try to buy them when they are cheap.