Back up your Images
It seems pretty obvious i know, everyone particularly photographers must back up their work/images etc. I have payed the price by not following that one simple rule. I normally back up every couple of days, having trouble with an external hard drive i had not backed up for quite some.
To cut a long story short i ended up loosing nearly two years worth of images that i will not be able to get back nor reproduce again.
I highly recommend backing up to a cloud service or get yourself a decent quality external hard drive, because once they are gone, they are gone.