Assuming I have no experience in running them, what would be called a good maintenance routine for a VPS server running mail server and LAMP with a couple of sites.

I've got one for quite a while now, but was doing what I feel is right without any guidance. It's ubuntu server and the only thing I do is ssh in there once a month and apt-get update, apt-get upgrade. Last year it suggested to update the distro, which I did. Waded through a bunch of diffs, broke mail server in the process and fixed it later on. So it turned out fine. Was this a right thing to do or should I stick with the old version just updating the packages?

Is there a difference in the routine if it will be Fedora?