What is the best way to store fresh berries?
Store them unwashed. Take out any "bad" ones. I've had decent luck adding some paper towels to wick away extra moisture that seems to speed up the spoilage. Martha Stewart suggest going even further and spreading them out on paper towels on a sheet pan. I have no idea who keeps a fridge empty enough that they can store full sheet pans in there, though.

I've never tried this, but someone suggests washing it lightly in vinegar/water. *shrug*

Then of course, wash and freeze them spread out on a sheet pan (to make it easier to separate later). I assume this isn't what you want to do, but it is very effective, depending on how you plan to use them.