Most responsible webmasters back up their blog from time to time. They understand that you never know what might happen. I think that most bloggers should probably back up their blog more often then they do. Anyway, the frequency of making backup is not what I wanted to discuss in this post. On the other hand, I want to explain some fundamental rules when it comes to backup. In particular, I want to say what you need to back up when it comes to your blog. In this case I will use a WordPress blog as an example:
Your blogs core files. Those are the files that are located on the server after your WordPress installation is finished. They might get corrupted, and backing up those files will ensure that you will be able to restore your blog easily. If you make any changes to those files, you will definitely want to back them up. Simply copy them to your hard drive and upload them if the files on the hosting server get corrupted.
Your blogs theme. This includes all modifications you made. Some bloggers put more work into their theme than others. However, even if you only made a few changes to your theme, it is crucial that you have a backup.
Your blogs plug-ins that you installed that are enabled or disabled. Finding the right plug-ins is time consuming, so you do not want them to get lost or corrupted. At least make a list of all plug-ins you have installed.
Images and files that are uploaded to your blog.