A network connection lets your computer communicate with the outside world, but it can also permit attackers in the outside world to reach into your computer and do damage. Therefore:
Decide whether or not the convenience of each Internet service is outweighed by its danger.
Know all of the services that your computer makes available on the network and remove or disable those that you think are too dangerous.
Pay specific attention to trap doors and Trojan horses that could compromise your internal network. For example, decide whether or not your users should be allowed to have .rhosts files. If you decide that they should not have such files, delete the files, rename the files, or modify your system software to disable the feature.