Always look for the ability to generate cash. Do not buy a business with no free cash flow in the near future. Any business is only valuable when it can generate free cash flow.
Sometimes you will lose cash in the short term but business can recover that cash in future. Such businesses are a good opportunity as an investor provided you are willing to hold for a long term.
Ability to understand future cash generation is the unfair advantage of an investor. I spend as much time possible to understand the cash flows of the company.
Study the growth in cash flow. You will understand why some stocks keep going up, in spite of expensive valuations.