As earnings season kicks into high gear, a long list of popular companies will be reporting their latest quarterly results next week. Three worth tuning into will be Apple (NASDAQ:AAPL), Tesla (NASDAQ:TSLA), and Amazon (NASDAQ:AMZN). Reports from these three major companies could spark big moves in any of their stock prices.

Ahead of these three earnings releases, here's a look at some key areas for each company that investors will want to watch.

The Apple storefront in Bangkok, Thailand.

Image source: Apple.

Apple

For Apple, the big story recently has been the company's worse-than-expected iPhone sales. This narrative started when the tech giant provided revenue guidance for its first quarter of fiscal 2019 that was below the consensus analyst estimate for the key metric. Some investors took this as a warning that sales of the company's latest iPhones were coming in lower than in the year-ago quarter.

Concerns about Apple's iPhone business were confirmed when the company announced preliminary revenue for the quarter that was $7 billion below the midpoint of management's guidance range for the key metric. The preliminary revenue figure implied a year-over-year revenue decline of about 5% -- and management said worse-than-expected iPhone sales in China were the main reason for the shortfall.

Since Apple has already reported preliminary revenue for its fiscal first quarter, investors should watch management's revenue guidance for its current quarter. This will help give investors an idea of how serious the company's iPhone problem is. Since iPhone accounts for over half of the tech giant's revenue, management's guidance for total revenue provides some insight into what management is expecting from its biggest product segment.

On average, analysts are expecting Apple to guide for first-quarter revenue of $59.3 billion, down from $61.1 billion in the same quarter in fiscal 2018. 

Apple is scheduled to report its fiscal first-quarter results on Tuesday, Jan. 29. 

Check out the latest Apple earnings call transcript.

Tesla

After swinging to a profit in its fourth quarter, the electric-car company's profitability will continue to be a major focus when Tesla reports its quarterly results next week. Third-quarter non-GAAP earnings per share jumped from a loss of $3.06 in the third quarter of 2017 to a profit of $2.90. 

A red Tesla Model 3.

Tesla's Model 3. Image source: Tesla.

For Tesla's fourth quarter, management recently said its profit for the period would be lower than it was in Q3. But the amount of the profit is unclear. Was Tesla able to generate a profit close to what it was in its third quarter? Or is it closer to breakeven?

Tesla will report its fourth-quarter results on Wednesday, Jan. 30. 

Check out the latest Tesla earnings call transcript.

Amazon

Investors will be watching Amazon's sales growth when the cloud-computing and e-commerce company reports its fourth-quarter results. Sales growth has recently decelerated significantly -- and the company's guidance for its recently ended fourth quarter implies even more deceleration.

Management said it expects revenue for the period to be between $66.5 billion and $72.5 billion, representing 10% to 20% year-over-year growth compared with the fourth quarter of 2017. Analysts, on average, expect revenue for the period to be $71.9 billion, translating to about 19% year-over-year growth.

Amazon reports its fourth-quarter results on Thursday, Jan. 31.

Check out the latest Amazon earnings call transcript.