Personally, my email account has never been hacked, but I know a few people whose email security has been compromised. One common mistake that all of them did was to put too little effort into making sure that their email account was well protected.
I have always believed and I will always believe that the owners of those accounts that have been compromised are to blame for the whole situation. Some email users have such ridiculously easy to guess passwords that they are just asking to be hacked. My advice is to make your password as complicated as possible. If you cannot remember it yourself, try to write it down in a safe place that nobody will have a chance to discover.