PWP's advice is thoughtful, but definitely overkill. Last time I checked, high-quality flash cards were rated for at least 100,000 write-erase cycles. Suppose it's just 1% of that; you'll have 1,000 uses of that card before it's worn out. That's almost 3 years of using it every day, at 1% of rated life.
>format in the camera I'm going to use it in
Yes, this is a good idea.
>never delete images off the card "in camera"
Me too, but not because of wear on the card; I do this because I don't want to accidentally erase the wrong image and/or I've got better things to do with a camera in my hand.
>never expose the cards to strong fields...meaning I don't put used cards in a pocket with a phone.
This is very unlikely. Flash memory is very robust, even able to survive x-ray machines just fine. If there's contrary evidence I'd appreciate seeing a reference.
>replace the cards after 18-24 months.
Overkill, as described above. Replace them when you need a bigger/faster card, or if you develop distrust for your card.
>I don't drop the cards.
Not dropping stuff is generally a good plan. They're tough, but if you treat them like glass you won't accidentally drop them down a storm sewer either.
>never use the cards in different devices. Canon EOS cameras only.
Overkill. So long as you reformat when you put it back in the camera, you're fine. If you tend to be forgetful about such things, then maybe you shouldn't use it in other devices.
>Download the images with a card reader, then extract it. Left in the computer it will continuously access the
>directory, checking the byte order, to see if there are any changes etc. This action is identical to a write cycle
> so the life of your card may be reduced.
This may have been true in the early days, but I'd be surprised (very surprised) if modern OS's aren't smart enough to avoid this. The best reason to pull it out right away is to make sure it gets back in your camera bag before you go out for a shoot.
>Don’t work on the image while it’s still on the card. You could possibly reduce the life expectancy
> of the card just by doing that with a single image.
Again, this is unlikely with modern wear-leveling algorithms. There's a better reason not to edit in-camera: the old adage "always make a backup of your original, and work only on copies." If you bork the image in-camera, it stays borked.
>Some say it's good practice not to fill a card completely.
I can see this somewhat: because file-size can vary quite a bit, you don't want to have the most recent image fail to save due to insufficient remaining space. It wouldn't cause the card itself to fail, just fail saving the image. Sure, pull the card out when you get to single-digit space remaining.
And again, my standard advice: "test, don't trust." Test new cards thoroughly before you use them. http://www.canonrumors.com/forum/index.php?topic=13413.msg241802#msg241802