For unprofitable tech companies, it's also important that the bottom line is moving from losses toward profits. As a company grows, it should become more efficient, especially when it comes to the sales and marketing spending necessary to close deals. If it's not, or if spending is growing as a percentage of revenue, that could indicate something is wrong.
Ultimately, a good tech stock is one that trades at a reasonable valuation, given its growth prospects. Accurately figuring out those growth prospects is the hard part. If you expect earnings to skyrocket in the coming years, paying a premium for the stock can make sense. But if you're wrong about those growth prospects, your investment may not work out.
Investing in an exchange-traded fund (ETF) that focuses on tech stocks is one way to avoid making mistakes. The iShares Expanded Tech Sector ETF (IGM -2.05%) is a comprehensive option at a 0.41% expense ratio.
Investing in tech stocks can be risky, but you can reduce your risk by investing only when you feel confident that their growth prospects justify their valuations.