With earnings season nearly upon us, it's a good time for investors to start deciding what companies' reports they'll want to check on. One stock I'll be watching this month is social network giant Facebook (META -0.95%). The tech giant's stock has slipped more than 14% over the past month as the negative press from The Wall Street Journal and an overall challenging period for growth stocks have weighed on shares.

With so much attention in the press, and considering the stock's recent slump, many people will likely be watching the social network's earnings report closely. Here are three metrics worth checking on when the report is released.

Facebook CEO Mark Zuckerberg discusses the company's 10-year roadmap at F8 2018

Facebook CEO Mark Zuckerberg. Image source: Facebook.

1. Daily active users

As always, investors should look for strong quarterly user engagement metrics. One of the best user metrics for gauging the company's ability to keep users engaged is its unique daily active users across its entire family of apps: Facebook, Instagram, Messenger, and WhatsApp. Facebook refers to this metric as its family daily active people (DAP).

This metric was 2.76 billion in Q2, up 12% year over year. Investors should look for a slight sequential increase and a similar year-over-year growth rate in this important metric. With users being the lifeblood of Facebook's business model, any sequential decrease or significant slowdown in its year-over-year growth rate for this metric could be a concern worth taking a closer look at.

2. Revenue growth

The company shouldn't have any trouble posting a strong revenue growth rate. Second-quarter revenue rose 56% year over year as the company was up against an easy comparison in the year-ago quarter, when many marketers paused or reduced their ad spend. But momentum is expected to persist in Q3 -- just at a slower yet very strong growth rate.

Analysts, on average, expect Facebook to post third-quarter revenue of $29.5 billion, up from revenue of $21.5 billion in the year-ago quarter. This translates to about 37% growth.

3. Expense guidance

Lately, Facebook has been benefiting from significant operating leverage. Its second-quarter operating margin, for example, was an astounding 43% -- up from 32% in the year-ago quarter. This helped net income more than double, increasing from $5.2 billion to $10.4 billion.

For the company to keep growing its operating margin, however, it's going to need to continue keeping expenses under control as a percentage of revenue. This is why investors should check on the company's guidance for full-year 2021 expenses. Previously, management said it expected total expenses this year to be between $70 billion and $73 billion.

"The year-over-year growth in expenses is driven primarily by investments in technical and product talent, infrastructure, and consumer hardware-related costs," said Facebook CFO Dave Wehner in the company's second-quarter earnings call.

Of course, investors should note that there could be a good case for higher-than-expected expense growth. After all, management also said in its second-quarter earnings call that its expense growth reflects the company's efforts "to invest ahead of the compelling long-term growth opportunities we see across our product portfolio."

Will Facebook maintain this outlook for expenses? Or will it change? If it did change, investors should look to the earnings call to find out why.

Facebook reports its earnings after market close on Monday, Oct. 25.