Scarcity drives, FOMO, and FOMO drives action. A few ways to tap into that: Highlight your existing leasing success; I.e. "Tours have already begun and spaces are filling up fast" creates a sense that they could miss out if they aren't quick.
If you have a ton of units or if it's obvious that you aren't going to fill up fast... you can do something similar with the available selection or inventory in a certain building filling up... We ran a campaign along the lines of "Apply today -- current inventory is at its largest now, and that won't last long..."
To that note you can also play into Limited Availability: for example, add a message on the site such as "Only a few apartments left in this building!"
Going further down the rabbit hole, campaigns and offers can be another way to create a sense of urgency if they are paired well with a hard end date. I.e. "Apply before 05/11/2024 and we'll cover your move-in costs" etc etc.
Lastly, add a sense of urgency in CTAs (call to action's) on your listings or website -- such as "Apply Now" or "Don't Miss Out - Apply Today!"
Hope this helps!