DCtoSC

I have recently started flying DCA-CHS on a regular basis. I think I already have 8 segments in the last four weeksas well as already having tickets booked for the next four weeks. I was wondering if people have advice for getting preferred status more quickly. My main concern is with being able to take standby flights without the hassle or fee. Right now I usually book the late flight on Thursday or Friday and try to get out as early as work will allow by going standby but it is expensive if you do it often. Any advice would be appreciated.