One of the most important things that you need to do with your site is to back it up.
Trust me there is nothing more frustrating than to have something happen to your site where the whole site gets messed up, and you need to start your whole site over.
If you have a backup then all you have to do is to re-install your site from your last backup. Then you only loose the information that you have added to your site since your last backup.
There are different ways to back up your site, the easiest way to do this is by
a plugin. My favorite paid backup plugin is called BackupBuddy, this is a very robust plugin. With BackupBuddy you can easily schedule daily, weekly, or even monthly backups and then store those backups in Dropbox, Amazon S3, Stash (their cloud service), or even just email it to yourself.
I like BackupBuddy because it is easy to use, and its not a subscription service. You buy a license and then you can use the plugin on as many sites as are allowed by your license. You have access to premium support forums, updates, and 1GB of their own cloud storage in which you can store your backups.
Another feature I really love is that you can use BackupBuddy to move WordPress to a new host with no Downtime.
My favored free backup program is BackupToDropbox. You can schedule when the backups will happen so its a set it and forget it plugin, which I love. The only drawback is the amount of storage that you have on DropBox, especially if you only a free account.
So your homework toady is to find a way to backup your site, and to back your site up. If you are unsure than I suggest you start with BackupToDropbox and then take your time and research what will work best for you. If you already are backing up your site, then your homework is to make sure your site really is backing up and then to clean up any old and severally out of date backups. No reason to have more than a handful of backups in different locations to secure your information.