Become good friends with CMs who are willing to book the rooms for you
Take advantage of the 40% off discounts on the website (although that's always very last minute)
Last year, we returned from DLP in January, to find an envelope at home from DLP with 40% off offers. The dates didn't work for us, but I kept that brochure until all dates were gone by... you never know when a last-minute trip comes up!