Keep your prices low. The biggest mistake people make is over-pricing. You won't get $2.00 each for romance novels- sell 'em for a quarter. Better to move a lot at low prices than one or two things at high dollar value. You will generate more excitement that way, get rid of the stuff you don't want to have to schlep to GoodWill anyway, and maybe you'll make someones day by helping them find a little treasure .
If you're doing this purely for profit, I suggest eBay as a better alternative.