Well I did PLC a long time ago when they split it up in summers between Camp Upsher and Brownsfield. I would say focus on your upper body development and running. Learn to climb ropes with your feet. And get used to two to four hours of sleep a night.
If you're going after you graduate, try to schedule a fall class. Quantico is too hot in the summer and being in the field during winter sucks. But you'll have to deal with that once you get to the Basic School. But it's best to avoid weather problems when you're trying to make the cut.
I would also like to add to focus on pull-ups, and when you run, do it with some sort of weight belt and a five-pound weight in your hand. You will usually do the run circuit with canteens around your waist and an M-16 in your hand. Don't neglect situps as I still think they are part of the PFT, or they might have gone to crunches now.
Oh, and if you can get yourself a pair of military boots, run in them. Get some insoles and take them to OCS with you. All your running will be in boots, except for your PFT's, (which are few and far between and are seen as a luxury, not as a hassle as they are before you get there).