Outflow equals inflow. Make phone calls, increase online ads, Resident referral offers on residents' doors, community bulletin boards, anything that outflows. Any outreach will create a vacuum and bring people in.
Answer the phone. Increase your package on apartments.com
(in most cases). Resident referral temporarily increased bonus. There are a ton of strategies depending on market and reason for lower demand.
Start a competition between leasing agents and add an extra commission to the most stale unit. Or better yet, hide a blue vase or something in one of the units and let them figure out which unit has the bonus commission blue vase while they tour. I've seen this generate better tours and increase conversions with just a little healthy competition. They get creative for you as far as sales and ads as part of the competition too.