Before exposing it to INTERNET. !!!!!
1: Your purposeLinux, like Microsoft Windows, is simply a computer operating system. When I talk to friends or co-workers who are embarking on the Linux experience for their initial time, this is the first point I stress. Linux in itself is not a magic wand that can be waved and make all sorts of computing problems disappear. While Windows has its own set of problems, so too does Linux. There is no such thing as a perfect or completely secure computer operating system. Will the machine be a desktop computer or a server; purpose is a key to understanding how to initially install and configure your Linux PC.
2: InstallationUnlike Windows, Linux does not present itself as a "server" version or as a "desktop" version. During a typical installation of Linux the choice is yours as to exactly what software you wish to install and therefore exactly what type of a system you are constructing. Because of this, you need to be aware of the packages that the installation program is installing for you. For example, some distributions will configure and start a Samba server or a mail server as part of the base install. Depending upon the purpose of your Linux PC and the security level you are prepared to accept, these services may not be needed or desired at all. Taking the time to familiarize yourself with your distributions' installer can prevent many headaches and/or reinstalls down the road.