1. Better to have more than one memory card than have a BIG one. 2-8 Gigs is the ideal capacity. You can size the card specifically for a camera. It is too risky to have all of your digital eggs in one basket.
2. Always format you card in your camera. Well, some said that by doing this, you will eventually reduce the capacity of the card. It is true, yet the main reason is not because of that. The structure of camera system is FAT 16 while the computer use FAT 32 or NTFS system.
3. Always format compact flash cards and microdrives in your camera. Also you should reformat the card every time you remove it from the camera. And most importantly, do not take the card out of your camera, check the images on a computer and then put the card back in the camera and continue shooting. You risk data loss.
4. Never fill a memory card or microdrive . If there is not enough space to write the last file, the entire card may get corrupted. Leave a few shots (three or four) at the end of each card. This greatly reduces the risk of card failure.