The best time to start preparing for a camping trip is when you put away from the previous one.  Take note of needed repairs (ripped tent screen), items that need replenishing (flashlight batteries, toothpaste), and gear that needs cleaning (camp stove, cook kit).

Wash your outdoor laundry and get it right back in your pack.  Clean your footware, and apply waterproofing. 

Get it done in the next day or two, or you’ll be up past midnight the night before you leave (at 6:00 AM) for your next adventure.  And when packing, pretend it is going to rain every day and night of your trip. 

I'm list maker, but I also like to journal on my trips.  So it's easy for me to jot down a few things as I go.  When I'm back home, I take a quick look at my notes, and take care of those items.