I always recommend formatting your memory card before a photo shoot (after you have saved the previous shoot's images of course). For Nikon DSLR users there is a simple shortcut available. Look on your camera for two green dots. They will be in slightly different positions depending on your model. Press the two buttons simultaneously and you will notice "for" will start flashing on your display. Press them again and your card will format. Your now ready for your photo shoot with a nice fresh card.