Earnings season is about to get social, with Facebook (NASDAQ:FB) and Twitter (NYSE:TWTR) earnings just around the corner. Facebook (NASDAQ:FB) will set the tone for Twitter, reporting results next week.

Facebook reports second-quarter results on Wednesday, July 23, after market close. The report will be followed by a live conference call. With the stock trading just 7% off all-time highs, and up 155% in the past year, you the stakes will be high when the social network announces its latest quarterly results. Hare the four most important metrics to watch when the numbers are released.

Facebook CEO Mark Zuckerberg in his conference room. Image source: Facebook.

Revenue growth
As usual, Facebook's revenue growth will take center stage. For an impressive four quarters in a row, Facebook has managed to boost its year-over-year revenue growth rates. In the company's most recent quarter, Facebook posted a record 72% year-over-year growth in revenue.

Analysts expect this growth to finally slow down this quarter, predicting the social network to report $2.81 billion in revenue, up 55% from the year-ago quarter. This growth rate would mark a significant reversal in growth -- and perhaps finally signal a peak to Facebook's accelerating growth rates.

Mobile revenue
As Facebook's advertising revenue continues to grow as a percentage of total ad revenue, investors will look for continued early success on this key front. In the company's most recent quarter, mobile ad revenue accounted for 59% of total ad revenue -- an all-time record for the company.

Data for chart retrieved from SEC filings for quarters shown.

Investors should look for mobile ad revenue to account for 62% or more of Facebook's total ad revenue, illustrating continued strength of the value proposition for mobile advertising to advertisers.

Daily active users
Facebook's greatest competitive advantage is its network effect. Its monstrous and unmatched user base of 802 million daily active users is what makes the platform so valuable to members.

Obviously the more active users Facebook has, the more powerful its user base is. Look for daily active users, therefore, to reach an all-time high of 834 million or more. This would mark a 4% sequential boost to daily active users, a sequential growth rate slightly lower than Q1's 6% growth.

When big growth expectations are priced into social stocks like Facebook and Twitter, user growth is paramount. This is the main concern that has irked investors regarding Twitter. Shares are down about 37% in the past six months on concerns that Twitter may not be able to grow users as fast as the Street originally thought. Though the company's most recent quarter's sequential growth in users of 6% is higher than Q4 2013's 4%, it still sits well below the growth Twitter was reporting in late 2012 and early 2013.

While Facebook obviously isn't expected to grow as fast as Twitter, user growth rates undoubtedly serves as a useful tool to investors in projecting business opportunity, going forward.

Engagement rate
As Facebook continues to make efforts to refine its portfolio of products available to advertisers, and tweak the way ads are shown, we want to know that customers are still just as engaged. Too many irrelevant ads, for instance, could prompt some users to use the service less -- or even leave.

Facebook mobile. Image source: Facebook.

So how do we measure engagement? Daily active users divided by monthly active users. In Facebook's most recent quarter, engagement hit 62.7%, up 120 basis points from the 61.5% in Q4.

Investors should look for Facebook to continue to improve this rate. A decline in this important metric could signal trouble. Look for 63% engagement or higher.

After Facebook's Q1 that blew past the most optimistic expectations for the company, the Street is likely hoping Facebook will provide some upside surprise. Indeed, given the company's wild price-to-earnings ratio of 85, the market seems to expect Facebook to find ways to continue exceed expectations over the long haul.

Can Facebook pull off another surprise quarter?