By posting again. Some days are also busier than others, for example a lot of people post on Fridays, and so the fresh section clears out pretty fast.
Growing your audience is a long-haul sort of thing, so keep posting with a consistent upload schedule, and try not to get discouraged.
As far as getting on Trending & Popular, it works with an algorithm. I don't think anyone knows the specifics of how it works but it's something along the lines of:
Views + Likes + Comments + New subscribers / Old subscribers = Your rank on trending/popular.
The trending tab does the calculation every couple of minutes, whereas the popular tab ranks things that have updated within the last 24 hours.
Keeping this in mind, a new series technically has an easier time getting to the top of trending/popular because it doesn't have as many old subscribers. If you can get a significant amount of attention right off the bat you can make it pretty high up the rankings.
There's also a thing called "the donut hole", which happens to series that have been established for awhile. This is when a series, despite having 100,000'nds of subscribers (usually a portion of that readerbase is inactive as well), can not create enough engagement during its new updates to break into trending/popular. You probably wont have to worry about this for awhile though.
Besides that, another good way to build your audience is to participate in conversations here on the forums (and elsewhere), and making friends with other cartoonists. You can also participate in self-promo threads, but I don't think these actually help much. The only one I post in is the "share your latest page" thread.
Be sure to link to your comic in your forum profile so if people like your posts they can find your stuff easily.
Best of luck! I hope this helped.