April marks the beginning of earnings season, particularly for tech investors. Some of the biggest names in tech will report earnings in April, including Apple, Google, Microsoft, and Facebook (NASDAQ:FB).

This week, Facebook gave a date to its first-quarter earnings report: April 22. Leading up to the report, here's a preview of the expectations as well as a close look at some of the key items beyond revenue and EPS worth watching when the company reports earnings.

Facebook will be one of the first tech giants to report earnings in April. Shares are up about 5% since the company reported fourth-quarter results in January and 31% in the past 12 months. The market will hold the company to high standards, expecting it to continue growing at robust rates.

Analysts, on average, expect Facebook to report record revenue of $3.56 billion, up 42% from the year-ago quarter. The consensus analyst estimate for Facebook's non-GAAP EPS is $0.40, up 18% from the year-ago quarter.

Here are a few other items to check on when Facebook reports first-quarter results.

Advertising revenue growth
Facebook's advertising revenue, which accounts for about 93% of the social network's total revenue, has been Facebook's primary driver in business growth since the company went public. But the year-over-year growth in this catalyst has been decelerating rapidly in recent quarters after peaking at 82% in the year-ago quarter.

In Q4, Facebook's year-over-year growth in ad revenue was 53%. With the company expected to report year-over-year total revenue growth of 42% in Q1, down from year-over-year growth in total revenue of 49% in Q4, investors should expect a similar sequential deceleration in Facebook's advertising revenue. For Q1, look for year-over-year advertising revenue growth of about 43%-49%.

Engagement rate
One of the most important metrics to keep an eye on when Facebook reports quarterly earnings is its user base's engagement rate, defined by daily active users, or DAUs divided by monthly active users, or MAUs. If Facebook's engagement rate ever begins to show a negative trend, it could signal that uses are finding Facebook less engaging or that they are increasingly turning to alternative platforms for sharing and connecting with friends and family.

Facebook's engagement rate in Q4 leveled off sequentially for the first time, at 64%. The company could very well report its first sequential decline in engagement in Q1. If Facebook does report its first sequential decline in engagement, investors should only be concerned if it's meaningful; engagement can't trend upward forever. Of course, if Facebook's user engagement rates continue to decline for more than one quarter, investors may have good reason to be concerned. But fluctuations around Facebook's peak engagement rate are bound to occur.

Look for an engagement rate of 63% or higher. Any further drop in Facebook's engagement rate could be a red flag.

Mobile daily active users
Of Facebook's user base, its mobile DAUs are the company's cream of the crop. On mobile, advertisements are more lucrative and engaging, making mobile users more valuable than desktop users when it comes to revenue generation. Facebook's growth in mobile DAUs has been the company's most important catalyst to advertising revenue growth.

In Q4, Facebook's mobile DAUs hit 745 million, up 34% from the year-ago quarter. This growth in mobile DAUs is a key reason for the surge in Facebook's mobile advertising revenue as a percentage of total advertising revenue.

Chart is based on data retrieved from SEC filings for quarters shown.

Look for Facebook's mobile DAUs to be around 782 million in Q1, up 5% sequentially -- one percentage point slower than the 6% sequential growth achieved in Q4.

Facebook's first-quarter financial results will be available to view here on Wednesday, April 22 shortly after market close.

Stay tuned at The Motley Fool for more pre-Facebook earnings analysis as well as our Foolish take on results when they are released.