The golden rule to backing up is to do so as often as you find practical. The more valuable the data, the more often you should back it up, and the more copies you should make. If your database gets updated at least once a day, you should really back it up on a daily basis. If, on the other hand, it is not updated very often, you could probably get by with less frequent backups.

You should consider making multiple backups and storing them in
different locations. If you have several servers, it is a simple matter
to copy your backups between them. You would also be well
advised to make physical backups on removable hard disks, thumb
drives, and so on, and to keep these in separate locations—preferably somewhere like a fireproof safe. It’s important to test restoring a database once in a while, too, to make sure your backups are done correctly. You also want to be familiar with restoring a database because you may have to do so when you are stressed and in a hurry, such as after a power failure that takes down the website. You can restore a database to a private server and run a few SQL commands to make sure the data is as you think it should be.