Instagram's popularity continues to soar: 500 million total users, 300 million of which use the app every single day. That's a powerful pool of potential fans. The question is how to best reach them. 

To see what some of the biggest brands are doing on Instagram, analytics firm TrackMaven analyzed a year's worth of Instagram posts--more than 41,000 in all--from Fortune 500 companies. They looked at the times of day brands post, along with the filters they use and other variables that can affect whether audiences interact with a post. 

Somewhat surprisingly, only half the companies are on Instagram, though that number is up from 24.6 percent in 2013. The champ?  Nike has 50 million followers, five times more than its nearest competitor on the list, Starbucks.

Here are four of the biggest takeaways from the analysis. You can view the full report here.

1. Comments are rare but valuable. 

While Facebook now offers a variety of ways to react to a post, Instagram keeps it simple: like or comment. The vast majority of interactions (98.9 percent) are likes, which suggests that getting your followers to chime in can be pretty difficult. But the payoff can be big, since these comments very often come in the form of users tagging their friends. (Read: free marketing!)

Inc. recently spoke with interior design startup Homepolish, which offered one strategy for high engagement on Instagram: Appeal to several different emotions to increase the likelihood your followers will tag each other. 

2. Filters matter. 

The vast majority of posts (89 percent) don't use any filter at all. Juno, Lark, and Clarendon tend to be the most widely used filters, even though they don't tend to draw the most engagement. Mayfair, Hefe, and Ludwig are the three filters that drive the most interactions, while "no filter" finished 13th. The bottom three engagement drivers are Moon, Inkwell, and Willow--Instagram's three black and white options. Those artsy colorless shots might make your personal feed look nice, but they don't quite hit home with wide audiences. 

3. The weekend is your friend.

Most Fortune 500 brands put up nearly double as many posts on the average weekday than on the average Saturday or Sunday. This doesn't mean you should follow suit--in fact, those weekend posts average 3 percent more audience engagement than ones posted on weekdays. With less competition, your weekend posts might be more likely to be seen by more eyes.

4. Mind the night owls.

Eighty-eight percent of Fortune 500 posts go up between 9 a.m. and 9 p.m. ET. Yes, people are most likely to be awake during this window, but the same against-the-grain principles can be applied here: Posts between 10 p.m. and 3 a.m. ET get between 6 and 9 percent more engagement than the average. This isn't to say you should wholly avoid peak daytime hours, but posting at a less competitive time can be an effective strategy. In the end, knowing your audience and performing your own analytics is the best way to understand what's really connecting with your followers--and creating a posting calendar is a good way to plan ahead.